Using mixins for animation based on @redmunds' feedback.

Author: larz0

src/styles/brackets.less

@@ -1282,7 +1282,7 @@ textarea.exclusions-editor {
     border-radius: 0 0 4px 4px;
     box-shadow: @tc-normal-shadow-bottom;
     opacity: 0;
-    -webkit-animation: autocomplete 90ms cubic-bezier(.01, .91, 0, .99) 0 1;
+    .animation (autocomplete, 90ms, cubic-bezier(.01, .91, 0, .99), 0, 1);
     -webkit-animation-fill-mode: forwards;
     -webkit-transform-origin: 0 0;
 

src/styles/brackets_mixins.less

@@ -141,3 +141,7 @@
     user-select: @type;
 }
 
+.animation (@name, @duration: 300ms, @ease: ease, @delay: 0, @iteration-count: 1) {
+	-webkit-animation: @name @duration @ease @delay @iteration-count;
+    animation: @name @duration @ease @delay @iteration-count;
+}

src/styles/brackets_patterns_override.less

@@ -231,7 +231,7 @@ a:focus {
 
 // Dropdown Menu Animation
 .dropdown-menu {
-    -webkit-animation: dropdown 90ms cubic-bezier(0, .97, .2, .99) 1;
+    .animation(dropdown, 90ms, cubic-bezier(0, .97, .2, .99), 0, 1);
     -webkit-transform-origin: 0 0;
 }
 
@@ -526,7 +526,7 @@ a:focus {
     position: relative;
     top: 0;
     margin: auto;
-    -webkit-animation: modal 240ms cubic-bezier(0, 1.05, .35, 1) 1;
+    .animation(modal, 240ms, cubic-bezier(0, 1.05, .35, 1), 0, 1);
 }
 
 .modal .close {
@@ -611,7 +611,7 @@ a:focus {
 }
 .last-backdrop {
     /* Only show the last modal backdrop */
-    -webkit-animation: backdrop 200ms linear 1;
+    .animation (backdrop, 200ms, linear, 0, 1);
     opacity: 0.4;
 }