diff --git a/app/javascript/mastodon/components/error_boundary.jsx b/app/javascript/mastodon/components/error_boundary.jsx
index 54424d283bc..e99461c821d 100644
--- a/app/javascript/mastodon/components/error_boundary.jsx
+++ b/app/javascript/mastodon/components/error_boundary.jsx
@@ -98,7 +98,7 @@ export default class ErrorBoundary extends PureComponent {
             )}
           </p>
 
-          <p className='error-boundary__footer'>Mastodon v{version} · <a href={source_url} rel='noopener' target='_blank'><FormattedMessage id='errors.unexpected_crash.report_issue' defaultMessage='Report issue' /></a> · <button onClick={this.handleCopyStackTrace} className={copied ? 'copied' : ''}><FormattedMessage id='errors.unexpected_crash.copy_stacktrace' defaultMessage='Copy stacktrace to clipboard' /></button></p>
+          <p className='error-boundary__footer'>Mastodon v{version} · <a href={source_url} rel='noopener' target='_blank'><FormattedMessage id='errors.unexpected_crash.report_issue' defaultMessage='Report issue' /></a> · <button type='button' onClick={this.handleCopyStackTrace} className={copied ? 'copied' : ''}><FormattedMessage id='errors.unexpected_crash.copy_stacktrace' defaultMessage='Copy stacktrace to clipboard' /></button></p>
         </div>
 
         <Helmet>
diff --git a/app/javascript/mastodon/components/media_gallery.jsx b/app/javascript/mastodon/components/media_gallery.jsx
index 1b0ee6d9588..ad55ce53c90 100644
--- a/app/javascript/mastodon/components/media_gallery.jsx
+++ b/app/javascript/mastodon/components/media_gallery.jsx
@@ -328,7 +328,7 @@ class MediaGallery extends PureComponent {
 
         {(visible && !uncached) && (
           <div className='media-gallery__actions'>
-            <button className='media-gallery__actions__pill' onClick={this.handleOpen}><FormattedMessage id='media_gallery.hide' defaultMessage='Hide' /></button>
+            <button type='button' className='media-gallery__actions__pill' onClick={this.handleOpen}><FormattedMessage id='media_gallery.hide' defaultMessage='Hide' /></button>
           </div>
         )}
       </div>
diff --git a/app/javascript/mastodon/components/status/legacy/content.jsx b/app/javascript/mastodon/components/status/legacy/content.jsx
index 908cf5be2e0..fee34b5f785 100644
--- a/app/javascript/mastodon/components/status/legacy/content.jsx
+++ b/app/javascript/mastodon/components/status/legacy/content.jsx
@@ -48,7 +48,7 @@ class TranslateButton extends PureComponent {
 
       return (
         <div className='translate-button'>
-          <button className='link-button' onClick={onClick}>
+          <button type='button' className='link-button' onClick={onClick}>
             <FormattedMessage id='status.show_original' defaultMessage='Show original' />
           </button>
 
@@ -60,7 +60,7 @@ class TranslateButton extends PureComponent {
     }
 
     return (
-      <button className='status__content__translate-button' onClick={onClick}>
+      <button type='button' className='status__content__translate-button' onClick={onClick}>
         <FormattedMessage id='status.translate' defaultMessage='Translate' />
       </button>
     );
@@ -198,7 +198,7 @@ class StatusContent extends PureComponent {
     });
 
     const readMoreButton = renderReadMore && (
-      <button className='status__content__read-more-button' onClick={this.props.onClick} key='read-more'>
+      <button type='button' className='status__content__read-more-button' onClick={this.props.onClick} key='read-more'>
         <FormattedMessage id='status.read_more' defaultMessage='Read more' /><Icon id='angle-right' icon={ChevronRightIcon} />
       </button>
     );
diff --git a/app/javascript/mastodon/features/notifications/components/clear_column_button.jsx b/app/javascript/mastodon/features/notifications/components/clear_column_button.jsx
index 73eaecba59f..13e099e1aa1 100644
--- a/app/javascript/mastodon/features/notifications/components/clear_column_button.jsx
+++ b/app/javascript/mastodon/features/notifications/components/clear_column_button.jsx
@@ -14,7 +14,7 @@ export default class ClearColumnButton extends PureComponent {
 
   render () {
     return (
-      <button className='text-btn column-header__setting-btn' tabIndex={0} onClick={this.props.onClick}><Icon id='eraser' icon={DeleteForeverIcon} /> <FormattedMessage id='notifications.clear' defaultMessage='Clear notifications' /></button>
+      <button type='button' className='text-btn column-header__setting-btn' tabIndex={0} onClick={this.props.onClick}><Icon id='eraser' icon={DeleteForeverIcon} /> <FormattedMessage id='notifications.clear' defaultMessage='Clear notifications' /></button>
     );
   }
 
diff --git a/app/javascript/mastodon/features/notifications/components/grant_permission_button.jsx b/app/javascript/mastodon/features/notifications/components/grant_permission_button.jsx
index cd46d878bbc..fc07eaeba42 100644
--- a/app/javascript/mastodon/features/notifications/components/grant_permission_button.jsx
+++ b/app/javascript/mastodon/features/notifications/components/grant_permission_button.jsx
@@ -11,7 +11,7 @@ export default class GrantPermissionButton extends PureComponent {
 
   render () {
     return (
-      <button className='text-btn column-header__permission-btn' tabIndex={0} onClick={this.props.onClick}>
+      <button type='button' className='text-btn column-header__permission-btn' tabIndex={0} onClick={this.props.onClick}>
         <FormattedMessage id='notifications.grant_permission' defaultMessage='Grant permission.' />
       </button>
     );
diff --git a/app/javascript/mastodon/features/notifications/requests.jsx b/app/javascript/mastodon/features/notifications/requests.jsx
index 4b20df50026..2ddcdf3885e 100644
--- a/app/javascript/mastodon/features/notifications/requests.jsx
+++ b/app/javascript/mastodon/features/notifications/requests.jsx
@@ -135,7 +135,7 @@ const SelectRow = ({selectAllChecked, toggleSelectAll, selectedItems, selectionM
         direction='right'
         title={intl.formatMessage(messages.more)}
       >
-        <button className='dropdown-button column-header__select-row__select-menu' disabled={selectedItems.length === 0}>
+        <button type='button' className='dropdown-button column-header__select-row__select-menu' disabled={selectedItems.length === 0}>
           <span className='dropdown-button__label'>
             {selectedCount} selected
           </span>
@@ -143,7 +143,7 @@ const SelectRow = ({selectAllChecked, toggleSelectAll, selectedItems, selectionM
         </button>
       </Dropdown>
       <div className='column-header__select-row__mode-button'>
-        <button className='text-btn' tabIndex={0} onClick={handleToggleSelectionMode}>
+        <button type='button' className='text-btn' tabIndex={0} onClick={handleToggleSelectionMode}>
           {selectionMode ? (
             <FormattedMessage id='notification_requests.exit_selection' defaultMessage='Done' />
           ) :