I installed Firefox 45 on a 2007 Dell Latitude with 2GB of RAM. It scrolls Wikipedia like a dream. The same machine chokes on modern Chromium or current Firefox.
Firefox 56 (late 2017) was the last version before Mozilla forced all extensions to move to the WebExtensions API. That switch broke thousands of legacy add-ons. Many were simple, quirky, powerful — and irreplaceable. old version firefox
Want tabs on the bottom, but really on the bottom? No problem. Want a status bar that shows link destinations without hovering? Done. Want to completely remove the address bar’s drop-down history? One tiny XUL script could do it. I installed Firefox 45 on a 2007 Dell