Flashify
Flashify is a browser extension for UXP/Legacy Firefox that forces select websites to run content in Adobe Flash Player instead of Ruffle..
ChromeTab
ChromeTab adds the ability to open a new tab type using an embedded Chromium renderer, in much the same vein as classic IE Tab for Firefox.
CustomTube-UXP
What if you could just choose your YouTube layout? Well, now you can! CustomTube lets you choose between recreations of any YouTube layout from 2008-2021, all with a single click! UXP compatible fork of the CustomTube WebExtension (WE by lightbeam24).