It was the final version to support legacy plugins like Silverlight and Java (excluding Adobe Flash), which were being phased out in favor of HTML5. The Quantum Leap:
Technically, yes, but you should not do it. Windows 11 requires modern security standards. Running an outdated browser on a modern OS is extremely dangerous. firefox version 52.9. 0 esr download
With the release of Firefox 57 (Quantum), Mozilla severed ties with the old extension framework (XUL/XPCOM). Suddenly, the "killer apps" that kept power users tethered to Firefox stopped working. The browser became faster, sleeker, and more Chrome-like, but for a specific demographic of users, it became a stranger. Firefox 52.9.0 ESR is the time capsule that preserves that lost functionality. For the die-hard power user, downloading 52.9.0 is not an act of stubbornness, but a refusal to accept a downgrade in capability in exchange for a shinier coat of paint. It was the final version to support legacy
If you still need to proceed, follow these steps to obtain the legitimate, unaltered installer: Running an outdated browser on a modern OS
