Since I use several Firefox profiles, it has been necessary for me to somehow identify the profile any given Firefox window belongs to. This extension allows you to customize the title bar. There are several variables available. Unfortunately, the Firefox profile name isn't one of them anymore, so you need to hard-code it in the extension's options tab. Apparently, the profile name *was* a variable several years ago, but a change to WebExtensions apparently made it unusable.

Nice!