Well, if they reproduce pre-Proton UI, Developer Tools and userChrome.css this way I'll just use it without complaints, despite being former diehard fan of Firefox. Because when they killed XUL addons and started messing with UI/UX every so often I stopped being one and now already consider it one of the Chrome average lookalikes on PC as there is no practical difference between using ungoogled Chromium (before manifest v3) and latest Firefox in my use-case. With Chromium being slightly better because I don't need to jump through hoops to install unpacked local addons there.