diff --git a/.eslintrc.js b/.eslintrc.js
index 9e965791b0..cbac530d6f 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -104,7 +104,6 @@ module.exports = {
     'react/jsx-equals-spacing': 'error',
     'react/jsx-no-bind': 'error',
     'react/jsx-no-target-blank': 'off',
-    'react/no-deprecated': 'off',
     'react/no-unknown-property': 'off',
     'react/self-closing-comp': 'error',
 
diff --git a/app/javascript/mastodon/components/autosuggest_input.jsx b/app/javascript/mastodon/components/autosuggest_input.jsx
index a68e2a01b4..218faabb79 100644
--- a/app/javascript/mastodon/components/autosuggest_input.jsx
+++ b/app/javascript/mastodon/components/autosuggest_input.jsx
@@ -154,7 +154,7 @@ export default class AutosuggestInput extends ImmutablePureComponent {
     this.input.focus();
   };
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (nextProps.suggestions !== this.props.suggestions && nextProps.suggestions.size > 0 && this.state.suggestionsHidden && this.state.focused) {
       this.setState({ suggestionsHidden: false });
     }
diff --git a/app/javascript/mastodon/components/autosuggest_textarea.jsx b/app/javascript/mastodon/components/autosuggest_textarea.jsx
index a627bc1ec2..50cc24b002 100644
--- a/app/javascript/mastodon/components/autosuggest_textarea.jsx
+++ b/app/javascript/mastodon/components/autosuggest_textarea.jsx
@@ -153,7 +153,7 @@ export default class AutosuggestTextarea extends ImmutablePureComponent {
     this.textarea.focus();
   };
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (nextProps.suggestions !== this.props.suggestions && nextProps.suggestions.size > 0 && this.state.suggestionsHidden && this.state.focused) {
       this.setState({ suggestionsHidden: false });
     }
diff --git a/app/javascript/mastodon/components/logo.jsx b/app/javascript/mastodon/components/logo.tsx
similarity index 75%
rename from app/javascript/mastodon/components/logo.jsx
rename to app/javascript/mastodon/components/logo.tsx
index 60e8f40b23..c3f409947a 100644
--- a/app/javascript/mastodon/components/logo.jsx
+++ b/app/javascript/mastodon/components/logo.tsx
@@ -1,15 +1,13 @@
 import React from 'react';
 import logo from 'mastodon/../images/logo.svg';
 
-export const WordmarkLogo = () => (
+export const WordmarkLogo: React.FC = () => (
   <svg viewBox='0 0 261 66' className='logo logo--wordmark' role='img'>
     <title>Mastodon</title>
     <use xlinkHref='#logo-symbol-wordmark' />
   </svg>
 );
 
-export const SymbolLogo = () => (
+export const SymbolLogo: React.FC = () => (
   <img src={logo} alt='Mastodon' className='logo logo--icon' />
 );
-
-export default WordmarkLogo;
diff --git a/app/javascript/mastodon/components/media_gallery.jsx b/app/javascript/mastodon/components/media_gallery.jsx
index 6bb3826408..564d6e7d55 100644
--- a/app/javascript/mastodon/components/media_gallery.jsx
+++ b/app/javascript/mastodon/components/media_gallery.jsx
@@ -241,7 +241,7 @@ class MediaGallery extends React.PureComponent {
     window.removeEventListener('resize', this.handleResize);
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (!is(nextProps.media, this.props.media) && nextProps.visible === undefined) {
       this.setState({ visible: displayMedia !== 'hide_all' && !nextProps.sensitive || displayMedia === 'show_all' });
     } else if (!is(nextProps.visible, this.props.visible) && nextProps.visible !== undefined) {
diff --git a/app/javascript/mastodon/components/modal_root.jsx b/app/javascript/mastodon/components/modal_root.jsx
index c0525c2217..7671d2725d 100644
--- a/app/javascript/mastodon/components/modal_root.jsx
+++ b/app/javascript/mastodon/components/modal_root.jsx
@@ -57,7 +57,7 @@ export default class ModalRoot extends React.PureComponent {
     this.history = this.context.router ? this.context.router.history : createBrowserHistory();
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (!!nextProps.children && !this.props.children) {
       this.activeElement = document.activeElement;
 
diff --git a/app/javascript/mastodon/features/account/components/account_note.jsx b/app/javascript/mastodon/features/account/components/account_note.jsx
index 5201ebd4dc..9a81b0aee2 100644
--- a/app/javascript/mastodon/features/account/components/account_note.jsx
+++ b/app/javascript/mastodon/features/account/components/account_note.jsx
@@ -22,7 +22,7 @@ class InlineAlert extends React.PureComponent {
 
   static TRANSITION_DELAY = 200;
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (!this.props.show && nextProps.show) {
       this.setState({ mountMessage: true });
     } else if (this.props.show && !nextProps.show) {
@@ -58,11 +58,11 @@ class AccountNote extends ImmutablePureComponent {
     saved: false,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this._reset();
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     const accountWillChange = !is(this.props.account, nextProps.account);
     const newState = {};
 
diff --git a/app/javascript/mastodon/features/audio/index.jsx b/app/javascript/mastodon/features/audio/index.jsx
index 56e913ae3a..5ed02d9378 100644
--- a/app/javascript/mastodon/features/audio/index.jsx
+++ b/app/javascript/mastodon/features/audio/index.jsx
@@ -136,7 +136,7 @@ class Audio extends React.PureComponent {
     }
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (!is(nextProps.visible, this.props.visible) && nextProps.visible !== undefined) {
       this.setState({ revealed: nextProps.visible });
     }
diff --git a/app/javascript/mastodon/features/blocks/index.jsx b/app/javascript/mastodon/features/blocks/index.jsx
index 38616ba844..da28f12d79 100644
--- a/app/javascript/mastodon/features/blocks/index.jsx
+++ b/app/javascript/mastodon/features/blocks/index.jsx
@@ -34,7 +34,7 @@ class Blocks extends ImmutablePureComponent {
     multiColumn: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchBlocks());
   }
 
diff --git a/app/javascript/mastodon/features/bookmarked_statuses/index.jsx b/app/javascript/mastodon/features/bookmarked_statuses/index.jsx
index 46fff856e4..1ffe7e768d 100644
--- a/app/javascript/mastodon/features/bookmarked_statuses/index.jsx
+++ b/app/javascript/mastodon/features/bookmarked_statuses/index.jsx
@@ -34,7 +34,7 @@ class Bookmarks extends ImmutablePureComponent {
     isLoading: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchBookmarkedStatuses());
   }
 
diff --git a/app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.jsx b/app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.jsx
index d428b2c4be..0b792418ff 100644
--- a/app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.jsx
+++ b/app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.jsx
@@ -59,7 +59,7 @@ class ModifierPickerMenu extends React.PureComponent {
     this.props.onSelect(e.currentTarget.getAttribute('data-index') * 1);
   };
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (nextProps.active) {
       this.attachListeners();
     } else {
diff --git a/app/javascript/mastodon/features/compose/components/privacy_dropdown.jsx b/app/javascript/mastodon/features/compose/components/privacy_dropdown.jsx
index dcc442a93b..82c738d9dd 100644
--- a/app/javascript/mastodon/features/compose/components/privacy_dropdown.jsx
+++ b/app/javascript/mastodon/features/compose/components/privacy_dropdown.jsx
@@ -214,7 +214,7 @@ class PrivacyDropdown extends React.PureComponent {
     this.props.onChange(value);
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     const { intl: { formatMessage } } = this.props;
 
     this.options = [
diff --git a/app/javascript/mastodon/features/domain_blocks/index.jsx b/app/javascript/mastodon/features/domain_blocks/index.jsx
index 0c22aa2396..6a9f6e4cf5 100644
--- a/app/javascript/mastodon/features/domain_blocks/index.jsx
+++ b/app/javascript/mastodon/features/domain_blocks/index.jsx
@@ -34,7 +34,7 @@ class Blocks extends ImmutablePureComponent {
     multiColumn: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchDomainBlocks());
   }
 
diff --git a/app/javascript/mastodon/features/favourited_statuses/index.jsx b/app/javascript/mastodon/features/favourited_statuses/index.jsx
index 2cbf002919..161297114d 100644
--- a/app/javascript/mastodon/features/favourited_statuses/index.jsx
+++ b/app/javascript/mastodon/features/favourited_statuses/index.jsx
@@ -34,7 +34,7 @@ class Favourites extends ImmutablePureComponent {
     isLoading: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchFavouritedStatuses());
   }
 
diff --git a/app/javascript/mastodon/features/favourites/index.jsx b/app/javascript/mastodon/features/favourites/index.jsx
index 4a8c1deb6f..ed210dad5b 100644
--- a/app/javascript/mastodon/features/favourites/index.jsx
+++ b/app/javascript/mastodon/features/favourites/index.jsx
@@ -31,13 +31,13 @@ class Favourites extends ImmutablePureComponent {
     intl: PropTypes.object.isRequired,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     if (!this.props.accountIds) {
       this.props.dispatch(fetchFavourites(this.props.params.statusId));
     }
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (nextProps.params.statusId !== this.props.params.statusId && nextProps.params.statusId) {
       this.props.dispatch(fetchFavourites(nextProps.params.statusId));
     }
diff --git a/app/javascript/mastodon/features/follow_requests/index.jsx b/app/javascript/mastodon/features/follow_requests/index.jsx
index a8875bbd31..779bc473e4 100644
--- a/app/javascript/mastodon/features/follow_requests/index.jsx
+++ b/app/javascript/mastodon/features/follow_requests/index.jsx
@@ -39,7 +39,7 @@ class FollowRequests extends ImmutablePureComponent {
     multiColumn: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchFollowRequests());
   }
 
diff --git a/app/javascript/mastodon/features/list_timeline/index.jsx b/app/javascript/mastodon/features/list_timeline/index.jsx
index c93305341a..e1408d8efb 100644
--- a/app/javascript/mastodon/features/list_timeline/index.jsx
+++ b/app/javascript/mastodon/features/list_timeline/index.jsx
@@ -76,7 +76,7 @@ class ListTimeline extends React.PureComponent {
     this.disconnect = dispatch(connectListStream(id));
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     const { dispatch } = this.props;
     const { id } = nextProps.params;
 
diff --git a/app/javascript/mastodon/features/lists/index.jsx b/app/javascript/mastodon/features/lists/index.jsx
index afd645a308..232b0c2d5a 100644
--- a/app/javascript/mastodon/features/lists/index.jsx
+++ b/app/javascript/mastodon/features/lists/index.jsx
@@ -42,7 +42,7 @@ class Lists extends ImmutablePureComponent {
     multiColumn: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchLists());
   }
 
diff --git a/app/javascript/mastodon/features/mutes/index.jsx b/app/javascript/mastodon/features/mutes/index.jsx
index 5c05d2f700..078d8779ec 100644
--- a/app/javascript/mastodon/features/mutes/index.jsx
+++ b/app/javascript/mastodon/features/mutes/index.jsx
@@ -35,7 +35,7 @@ class Mutes extends ImmutablePureComponent {
     multiColumn: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchMutes());
   }
 
diff --git a/app/javascript/mastodon/features/notifications/index.jsx b/app/javascript/mastodon/features/notifications/index.jsx
index 8a31c5db6c..8b77374c40 100644
--- a/app/javascript/mastodon/features/notifications/index.jsx
+++ b/app/javascript/mastodon/features/notifications/index.jsx
@@ -93,7 +93,7 @@ class Notifications extends React.PureComponent {
     trackScroll: true,
   };
 
-  componentWillMount() {
+  UNSAFE_componentWillMount() {
     this.props.dispatch(mountNotifications());
   }
 
diff --git a/app/javascript/mastodon/features/pinned_statuses/index.jsx b/app/javascript/mastodon/features/pinned_statuses/index.jsx
index 24a0b6d2e3..e58ce2bb89 100644
--- a/app/javascript/mastodon/features/pinned_statuses/index.jsx
+++ b/app/javascript/mastodon/features/pinned_statuses/index.jsx
@@ -29,7 +29,7 @@ class PinnedStatuses extends ImmutablePureComponent {
     multiColumn: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchPinnedStatuses());
   }
 
diff --git a/app/javascript/mastodon/features/reblogs/index.jsx b/app/javascript/mastodon/features/reblogs/index.jsx
index fb503f40f1..757ef0dd0e 100644
--- a/app/javascript/mastodon/features/reblogs/index.jsx
+++ b/app/javascript/mastodon/features/reblogs/index.jsx
@@ -31,13 +31,13 @@ class Reblogs extends ImmutablePureComponent {
     intl: PropTypes.object.isRequired,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     if (!this.props.accountIds) {
       this.props.dispatch(fetchReblogs(this.props.params.statusId));
     }
   }
 
-  componentWillReceiveProps(nextProps) {
+  UNSAFE_componentWillReceiveProps(nextProps) {
     if (nextProps.params.statusId !== this.props.params.statusId && nextProps.params.statusId) {
       this.props.dispatch(fetchReblogs(nextProps.params.statusId));
     }
diff --git a/app/javascript/mastodon/features/status/components/card.jsx b/app/javascript/mastodon/features/status/components/card.jsx
index 1d5edfc173..bc02665311 100644
--- a/app/javascript/mastodon/features/status/components/card.jsx
+++ b/app/javascript/mastodon/features/status/components/card.jsx
@@ -66,7 +66,7 @@ export default class Card extends React.PureComponent {
     revealed: !this.props.sensitive,
   };
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (!Immutable.is(this.props.card, nextProps.card)) {
       this.setState({ embedded: false, previewLoaded: false });
     }
diff --git a/app/javascript/mastodon/features/status/index.jsx b/app/javascript/mastodon/features/status/index.jsx
index 9a244c8be1..7a14761c44 100644
--- a/app/javascript/mastodon/features/status/index.jsx
+++ b/app/javascript/mastodon/features/status/index.jsx
@@ -209,7 +209,7 @@ class Status extends ImmutablePureComponent {
     loadedStatusId: undefined,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     this.props.dispatch(fetchStatus(this.props.params.statusId));
   }
 
@@ -217,7 +217,7 @@ class Status extends ImmutablePureComponent {
     attachFullscreenListener(this.onFullScreenChange);
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (nextProps.params.statusId !== this.props.params.statusId && nextProps.params.statusId) {
       this._scrolledIntoView = false;
       this.props.dispatch(fetchStatus(nextProps.params.statusId));
diff --git a/app/javascript/mastodon/features/ui/components/bundle.jsx b/app/javascript/mastodon/features/ui/components/bundle.jsx
index 1b10a218b6..c1e837b16e 100644
--- a/app/javascript/mastodon/features/ui/components/bundle.jsx
+++ b/app/javascript/mastodon/features/ui/components/bundle.jsx
@@ -33,11 +33,11 @@ class Bundle extends React.PureComponent {
     forceRender: false,
   };
 
-  componentWillMount() {
+  UNSAFE_componentWillMount() {
     this.load(this.props);
   }
 
-  componentWillReceiveProps(nextProps) {
+  UNSAFE_componentWillReceiveProps(nextProps) {
     if (nextProps.fetchComponent !== this.props.fetchComponent) {
       this.load(nextProps);
     }
diff --git a/app/javascript/mastodon/features/ui/components/columns_area.jsx b/app/javascript/mastodon/features/ui/components/columns_area.jsx
index 1ce14b4c5b..346f44bf09 100644
--- a/app/javascript/mastodon/features/ui/components/columns_area.jsx
+++ b/app/javascript/mastodon/features/ui/components/columns_area.jsx
@@ -78,7 +78,7 @@ export default class ColumnsArea extends ImmutablePureComponent {
     this.isRtlLayout = document.getElementsByTagName('body')[0].classList.contains('rtl');
   }
 
-  componentWillUpdate(nextProps) {
+  UNSAFE_componentWillUpdate(nextProps) {
     if (this.props.singleColumn !== nextProps.singleColumn && nextProps.singleColumn) {
       this.node.removeEventListener('wheel', this.handleWheel);
     }
diff --git a/app/javascript/mastodon/features/ui/components/navigation_panel.jsx b/app/javascript/mastodon/features/ui/components/navigation_panel.jsx
index ee1a83cc60..b62d216ae9 100644
--- a/app/javascript/mastodon/features/ui/components/navigation_panel.jsx
+++ b/app/javascript/mastodon/features/ui/components/navigation_panel.jsx
@@ -2,7 +2,7 @@ import React from 'react';
 import PropTypes from 'prop-types';
 import { defineMessages, injectIntl } from 'react-intl';
 import { Link } from 'react-router-dom';
-import Logo from 'mastodon/components/logo';
+import { WordmarkLogo } from 'mastodon/components/logo';
 import { timelinePreview, showTrends } from 'mastodon/initial_state';
 import ColumnLink from './column_link';
 import DisabledAccountBanner from './disabled_account_banner';
@@ -46,7 +46,7 @@ class NavigationPanel extends React.Component {
     return (
       <div className='navigation-panel'>
         <div className='navigation-panel__logo'>
-          <Link to='/' className='column-link column-link--logo'><Logo /></Link>
+          <Link to='/' className='column-link column-link--logo'><WordmarkLogo /></Link>
           <hr />
         </div>
 
diff --git a/app/javascript/mastodon/features/ui/index.jsx b/app/javascript/mastodon/features/ui/index.jsx
index 5bbd94c268..df6a1b3fa2 100644
--- a/app/javascript/mastodon/features/ui/index.jsx
+++ b/app/javascript/mastodon/features/ui/index.jsx
@@ -126,7 +126,7 @@ class SwitchingColumnsArea extends React.PureComponent {
     mobile: PropTypes.bool,
   };
 
-  componentWillMount () {
+  UNSAFE_componentWillMount () {
     if (this.props.mobile) {
       document.body.classList.toggle('layout-single-column', true);
       document.body.classList.toggle('layout-multiple-columns', false);
diff --git a/app/javascript/mastodon/features/video/index.jsx b/app/javascript/mastodon/features/video/index.jsx
index 8b57cf3d10..3d9d1aec6c 100644
--- a/app/javascript/mastodon/features/video/index.jsx
+++ b/app/javascript/mastodon/features/video/index.jsx
@@ -370,7 +370,7 @@ class Video extends React.PureComponent {
     }
   }
 
-  componentWillReceiveProps (nextProps) {
+  UNSAFE_componentWillReceiveProps (nextProps) {
     if (!is(nextProps.visible, this.props.visible) && nextProps.visible !== undefined) {
       this.setState({ revealed: nextProps.visible });
     }
diff --git a/app/javascript/mastodon/store/index.ts b/app/javascript/mastodon/store/index.ts
index 6c3e963d9e..f7e1be6b7b 100644
--- a/app/javascript/mastodon/store/index.ts
+++ b/app/javascript/mastodon/store/index.ts
@@ -8,7 +8,21 @@ import { TypedUseSelectorHook, useDispatch, useSelector } from 'react-redux';
 export const store = configureStore({
   reducer: rootReducer,
   middleware: (getDefaultMiddleware) =>
-    getDefaultMiddleware()
+    getDefaultMiddleware({
+      // In development, Redux Toolkit enables 2 default middlewares to detect
+      // common issues with states. Unfortunately, our use of ImmutableJS for state
+      // triggers both, so lets disable them until our state is fully refactored
+
+      // https://redux-toolkit.js.org/api/serializabilityMiddleware
+      // This checks recursively that every values in the state are serializable in JSON
+      // Which is not the case, as we use ImmutableJS structures, but also File objects
+      serializableCheck: false,
+
+      // https://redux-toolkit.js.org/api/immutabilityMiddleware
+      // This checks recursively if every value in the state is immutable (ie, a JS primitive type)
+      // But this is not the case, as our Root State is an ImmutableJS map, which is an object
+      immutableCheck: false,
+    })
       .concat(
         loadingBarMiddleware({
           promiseTypeSuffixes: ['REQUEST', 'SUCCESS', 'FAIL'],