Firefox - remove ugly Proton UI

linux/firefox.md

@@ -1,5 +1,65 @@
 # Firefox
 
+## Reset ugly Proto UI
+
+First you need to enable custom CSS by opening "about:config" in a tab. There you need to set the option `toolkit.legacyUserProfileCustomizations.stylesheets` to `true`.
+
+Afterwards you need to create a directory called `chrome` (sic!) in your Firefox profile directory. In there you need a file called `userChrome.css`.
+
+The following content of the file will make it look more like the old Firefox UI:
+
+```css
+.titlebar-color {
+  color: -moz-accent-color-foreground;
+  background-color: -moz-accent-color;
+}
+
+.tab-background {
+  border-radius: 0px 0px !important;
+  margin-bottom: 0px !important;
+}
+
+.tabbrowser-tab:not([selected="true"]):not([multiselected="true"]) .tab-background {
+  background-color: color-mix(in srgb, currentColor 5%, transparent);
+}
+
+.tabbrowser-tab:not([selected="true"]) > .tab-stack > .tab-background {
+  border: 1px solid rgba(130, 130, 130, 0.5) !important;
+}
+
+.tabbrowser-tab[selected="true"] .tab-background {
+  border-top: 3px solid #3daee9 !important;
+  border-left: 1px solid rgba(130, 130, 130, 0.5) !important;
+  border-right: 1px solid rgba(130, 130, 130, 0.5) !important;
+}
+
+.toolbar-items, .tabbrowser-tab {
+  max-height: 38px;
+}
+
+:root[uidensity=touch] .toolbar-items, .tabbrowser-tab {
+  max-height: 45px;
+}
+
+.tabbrowser-tab[usercontextid] .tab-background {
+  background: var(--identity-tab-color) !important;
+  border-left: 1px solid rgba(130, 130, 130, 0.5) !important;
+  border-right: 1px solid rgba(130, 130, 130, 0.5) !important;
+  border-bottom: var(--identity-tab-color) !important;
+  opacity: 0.8 !important;
+}
+
+menupopup > menu, menupopup > menuitem {
+  padding-block: 2px !important;
+}
+
+:root {
+  --arrowpanel-menuitem-padding: 2px !important;
+}
+```
+
+For a description of what this CSS does please see the original [source](https://www.dedoimedo.com/computers/firefox-91-disable-proton.html).
+
 ## Enable use of flash player plugin
 
 **WARNING**: You are creating a Firefox browser which can use **deprecated**, **unsafe** plugins like Flash or Java. Please keep in mind to only access safe webpages with it. **You have been warned!**