diff --git a/client/scss/components/_forms.scss b/client/scss/components/_forms.scss
index 7c918c5cd9..4b6185bfdc 100644
--- a/client/scss/components/_forms.scss
+++ b/client/scss/components/_forms.scss
@@ -74,11 +74,6 @@
 //     }
 // }
 
-// Reset the arrow on `<select>`s in IE10+.
-select::-ms-expand {
-  display: none;
-}
-
 // select boxes
 .collection_choice_field .input,
 .choice_field .input,
diff --git a/client/scss/components/_main-nav.scss b/client/scss/components/_main-nav.scss
index b07ebec1c2..f36c0daaef 100644
--- a/client/scss/components/_main-nav.scss
+++ b/client/scss/components/_main-nav.scss
@@ -553,48 +553,3 @@ footer,
     z-index: 200;
   }
 }
-
-///////////////////////
-// Media query hacks //
-///////////////////////
-
-// to detect IE10+ which doesn't support 3d transform of static elements and needs a fallback
-// stylelint-disable scss/media-feature-value-dollar-variable
-@media all and (-ms-high-contrast: none), all and (-ms-high-contrast: active) {
-  .wrapper {
-    @include transition(left 0.2s ease);
-    left: 0;
-  }
-
-  body.nav-open {
-    .wrapper {
-      transform: none;
-      left: $menu-width;
-      position: relative;
-    }
-  }
-
-  body.explorer-open {
-    .wrapper {
-      transform: none;
-      left: $menu-width-max;
-    }
-
-    .nav-wrapper {
-      width: $menu-width-max;
-    }
-  }
-}
-
-@media all and (min-width: breakpoint-min(sm)) and (-ms-high-contrast: none),
-  all and (min-width: breakpoint-min(sm)) and (-ms-high-contrast: active) {
-  body.explorer-open {
-    .wrapper {
-      left: 0;
-    }
-
-    .nav-wrapper {
-      width: $menu-width;
-    }
-  }
-}
diff --git a/client/scss/components/_switch.scss b/client/scss/components/_switch.scss
index 815909f03f..f60d9c2f40 100644
--- a/client/scss/components/_switch.scss
+++ b/client/scss/components/_switch.scss
@@ -77,7 +77,6 @@ $switch-color-middle-grey: #777;
 
   [type='checkbox']:focus + &__toggle {
     outline: $color-focus-outline solid $switch-outline;
-    -moz-outline-radius: $switch-outline-radius;
   }
 
   [type='checkbox'] {
diff --git a/client/scss/elements/_forms.scss b/client/scss/elements/_forms.scss
index ad06450ae3..36256e12f1 100644
--- a/client/scss/elements/_forms.scss
+++ b/client/scss/elements/_forms.scss
@@ -123,11 +123,6 @@ select,
   }
 }
 
-// Reset the arrow on `<select>`s in IE10+.
-select::-ms-expand {
-  display: none;
-}
-
 .file_field {
   .input {
     label {
diff --git a/client/src/components/CommentApp/components/CommentHeader/style.scss b/client/src/components/CommentApp/components/CommentHeader/style.scss
index f096711e69..f994035702 100644
--- a/client/src/components/CommentApp/components/CommentHeader/style.scss
+++ b/client/src/components/CommentApp/components/CommentHeader/style.scss
@@ -40,9 +40,7 @@
     }
 
     > button,
-    > details > summary,
-    .details-fallback > .details-fallback__summary {
-      // IE11 uses divs instead with these classes
+    > details > summary {
       // Hides triangle on Firefox
       list-style-type: none;
       // Hides triangle on Chrome
@@ -54,7 +52,6 @@
       position: relative;
       background-color: unset;
       border: unset;
-      -moz-outline-radius: 10px;
       padding: 0;
       box-sizing: border-box;
 
@@ -71,9 +68,7 @@
       }
     }
 
-    > details,
-    > .details-fallback {
-      // IE11 uses divs instead with these classes
+    > details {
       position: relative;
 
       > div {
@@ -85,9 +80,7 @@
 
     &--more {
       > button,
-      > details > summary,
-      > .details-fallback > .details-fallback__summary {
-        // IE11 uses divs instead with these classes
+      > details > summary {
         color: #767676;
 
         // stylelint-disable-next-line max-nesting-depth
@@ -140,12 +133,3 @@
 .comment-reply--mode-deleting .comment-header {
   opacity: 0.5;
 }
-
-// IE11 only uses these classes
-.details-fallback .comment-header__more-actions {
-  display: none;
-}
-
-.details-fallback--open .comment-header__more-actions {
-  display: block;
-}
diff --git a/client/src/components/CommentApp/main.scss b/client/src/components/CommentApp/main.scss
index d34fa9a561..e1d71f2d7f 100644
--- a/client/src/components/CommentApp/main.scss
+++ b/client/src/components/CommentApp/main.scss
@@ -48,7 +48,6 @@ $box-padding: 10px;
     border: 1px solid $color-textarea-border;
     box-sizing: border-box;
     border-radius: 5px;
-    -moz-outline-radius: 8px;
     color: $color-box-text;
 
     &::placeholder {
@@ -101,7 +100,6 @@ $box-padding: 10px;
   background-color: inherit;
   border: 1px solid $color-grey-3;
   border-radius: 3px;
-  -moz-outline-radius: 6px;
   color: $color-teal;
   cursor: pointer;
   text-transform: uppercase;
diff --git a/client/src/components/Explorer/Explorer.scss b/client/src/components/Explorer/Explorer.scss
index c897bf19e6..5c570777a2 100644
--- a/client/src/components/Explorer/Explorer.scss
+++ b/client/src/components/Explorer/Explorer.scss
@@ -168,11 +168,6 @@ $menu-footer-height: 50px;
       background-color: inherit;
       cursor: inherit;
     }
-
-    // Reset the arrow on `<select>`s in IE10+.
-    &::-ms-expand {
-      display: none;
-    }
   }
 
   // Add select arrow back on browsers where native ui has been removed
diff --git a/client/src/components/PageExplorer/PageExplorer.scss b/client/src/components/PageExplorer/PageExplorer.scss
index 7f78398e23..cee8289244 100644
--- a/client/src/components/PageExplorer/PageExplorer.scss
+++ b/client/src/components/PageExplorer/PageExplorer.scss
@@ -127,11 +127,6 @@ $explorer-header-horizontal-padding: 10px;
       background-color: inherit;
       cursor: inherit;
     }
-
-    // Reset the arrow on `<select>`s in IE10+.
-    &::-ms-expand {
-      display: none;
-    }
   }
 
   // Add select arrow back on browsers where native ui has been removed
diff --git a/docs/_static/css/custom.css b/docs/_static/css/custom.css
index bab8d0d2e9..c866c2c8e5 100644
--- a/docs/_static/css/custom.css
+++ b/docs/_static/css/custom.css
@@ -92,12 +92,12 @@ details {
   background: none;
 }
 
-/* Bounce the UFO on hover  */
 @keyframes bounce {
   0%,
   100% {
     transform: translateY(0);
   }
+
   50% {
     transform: translateY(-5px);
   }
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss b/wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss
index 8a027a7a25..7e964fe637 100644
--- a/wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss
+++ b/wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss
@@ -531,15 +531,11 @@ footer .preview {
       flex-flow: row-reverse wrap;
 
       &_small-part {
-        // IE11 requires units on the flex basis. Unitless breaks.
-        // stylelint-disable-next-line length-zero-no-unit
-        flex: 1 0 0%;
+        flex: 1 0 0;
       }
 
       &_big-part {
-        // IE11 requires units on the flex basis. Unitless breaks.
-        // stylelint-disable-next-line length-zero-no-unit
-        flex: 5 0 0%;
+        flex: 5 0 0;
       }
     }
 
diff --git a/wagtail/contrib/redirects/static/wagtailredirects/css/index.css b/wagtail/contrib/redirects/static/wagtailredirects/css/index.css
index 3ca39cd7ce..63f53c662f 100644
--- a/wagtail/contrib/redirects/static/wagtailredirects/css/index.css
+++ b/wagtail/contrib/redirects/static/wagtailredirects/css/index.css
@@ -5,10 +5,6 @@
 }
 
 header .has-multiple-actions {
-    display: -webkit-box;
-    display: -moz-box;
-    display: -webkit-flex;
-    display: -ms-flexbox;
     display: flex;
 }
 
diff --git a/wagtail/project_template/home/static/css/welcome_page.css b/wagtail/project_template/home/static/css/welcome_page.css
index ce8b1497f5..2b1687c187 100644
--- a/wagtail/project_template/home/static/css/welcome_page.css
+++ b/wagtail/project_template/home/static/css/welcome_page.css
@@ -40,10 +40,6 @@ ul {
     font-weight: 400;
 }
 
-main {
-    display: block; /* For IE11 support */
-}
-
 svg:not(:root) {
     overflow: hidden;
 }
@@ -85,36 +81,20 @@ svg:not(:root) {
     max-width: 265px;
 }
 
-@-webkit-keyframes pos {
-    0%, 100% {
-        -webkit-transform: rotate(-6deg);
-        transform: rotate(-6deg);
-    }
-    50% {
-        -webkit-transform: rotate(6deg);
-        transform: rotate(6deg);
-    }
-}
-
 @keyframes pos {
     0%, 100% {
-        -webkit-transform: rotate(-6deg);
         transform: rotate(-6deg);
     }
     50% {
-        -webkit-transform: rotate(6deg);
         transform: rotate(6deg);
     }
 }
 
 .egg {
     fill: #43b1b0;
-    -webkit-animation: pos 3s ease infinite;
-            animation: pos 3s ease infinite;
-    -webkit-transform: translateY(50px);
-            transform: translateY(50px);
-    -webkit-transform-origin: 50% 80%;
-            transform-origin: 50% 80%;
+    animation: pos 3s ease infinite;
+    transform: translateY(50px);
+    transform-origin: 50% 80%;
 }
 
 .main-text {