The new proton interface does not change the bookmarks.

What kind of change were you expecting to see?

It is a little odd that the separator line above "Open All in Tabs" is not in a contrasting color.

Sorry for not being clear enough.

I just want Firefox on Linux to have the same UI as on Windows. I have added a new screenshot showing the difference between the two.

I've done some research and I think I've found the problem, it's the GTK Pop theme that replaces the default theme, I don't know how to remove it.

I tried to change "widget.content.gtk-theme-override" in about:config, but it doesn't work. (widget.content.gtk-theme-override is set on Pop by default)

I changed: "toolkit.legacyUserProfileCustomizations.stylesheets" to "true". I created a "chrome/userContent.css" file in my profile :

input:not(.urlbar-input):not(.textbox-input):not(.form-control):not([type='checkbox']):not([type='radio']), textarea, select {

   -moz-appearance: none !important;

}

It does not work either

The context menu and bookmark bar changes when I change the global theme of GTK via gnome tweaks So I would like to find a way to disable the GTK theme for firefox only.

I don't think it's a Firefox problem but rather a GTK problem. I will install Fedora to see if I have the same problem.

Does your about:config show a preference named widget.non-native-theme.enabled ? I'm not sure what it does, actually, but I think it affects how closely Firefox follows your OS theme.

There are a bunch of preferences starting with widget.non-native-theme. that might be relevant in some way...

In my about:config, the preference widget.non-native-theme.enabled is set to true.

I tried changing the preferences with booleans from true to false in widget.non-native-theme. It does not change anything.