Whenever possible, run your legacy Firefox versions inside an isolated Virtual Machine (using software like VirtualBox or VMware) running Windows XP or Windows 7 with network adapter access strictly restricted.
Modern browsers have almost universally removed support for NPAPI plugins due to severe security risks. . Certain specialized university courses, legacy trading platforms, and old, custom-built intranet sites were built on Java and have never been updated. For these environments, an old version of Firefox is the only way to access them. Download Firefox 12-51 52 Esr
Brought significant performance overhauls, including SPDY protocol support by default, a revamped New Tab page, and the integration of the developer command line. Whenever possible, run your legacy Firefox versions inside