use unprefixed CSS user-select, available since Chrome 54

install-usercss/install-usercss.css

@@ -288,9 +288,7 @@ li {
 
 #header:not(.meta-init) > *:not(.lds-spinner),
 #header.meta-init > .lds-spinner {
-  -webkit-user-select: none;
   -moz-user-select: none;
-  -ms-user-select: none;
   user-select: none;
   pointer-events: none;
   opacity: 0;
@@ -299,9 +297,7 @@ li {
 #header.meta-init > * {
   opacity: 1;
   transition: opacity .5s;
-  -webkit-user-select: auto;
   -moz-user-select: auto;
-  -ms-user-select: auto;
   user-select: auto;
 }
 

options/onoffswitch.css

@@ -3,9 +3,8 @@
 .onoffswitch {
   position: relative;
   margin: 1ex 0;
-  -webkit-user-select: none;
   -moz-user-select: none;
-  -ms-user-select: none;
+  user-select: none;
 }
 
 .onoffswitch input {

popup/search-results.css

@@ -271,9 +271,7 @@ body.search-results-shown {
 
 /* spinner: https://github.com/loadingio/css-spinner */
 .lds-spinner {
-  -webkit-user-select: none;
   -moz-user-select: none;
-  -ms-user-select: none;
   user-select: none;
   pointer-events: none;
   position: absolute;

vendor-overwrites/colorpicker/colorpicker.css

@@ -86,10 +86,7 @@
   border: 1px solid var(--main-border-color);
   background-color: var(--main-background-color);
   box-shadow: 0 0 10px 0 rgba(0, 0, 0, 0.12);
-  -webkit-user-select: none;
   -moz-user-select: none;
-  -ms-user-select: none;
-  -o-user-select: none;
   user-select: none;
 }
 
@@ -295,10 +292,7 @@
   font-size: 11px;
   font-weight: bold;
   box-sizing: border-box;
-  -webkit-user-select: text;
   -moz-user-select: text;
-  -ms-user-select: text;
-  -o-user-select: text;
   user-select: text;
   border: 1px solid var(--input-border-color);
   background-color: var(--input-background-color);