If you install an older version, Firefox will immediately try to update to the latest version. To stop this: Go to Options (or Preferences ). Navigate to General . Scroll down to Firefox Updates .
Never use a legacy browser for banking, shopping, or accessing sensitive personal data.
These versions belong to the era before Firefox began rapid versioning and Quantum architectural changes. They are fast but lack modern security patches and advanced web technologies (like newer CSS and HTML5 specifications). Firefox 52 ESR (Extended Support Release) Download Firefox 12-51 52 Esr
Older hardware running Snow Leopard, Lion, or Mountain Lion cannot run modern Chromium or Firefox builds.
: It supports older "XUL" based extensions that were disabled in Firefox 57 (Quantum). Important Security Warning If you install an older version, Firefox will
Before Firefox Quantum (version 57), the browser supported a different type of extension system (XUL/XPCOM). Users who rely on legacy add-ons often need to roll back to versions before 57.
Released in early 2017, Firefox 52 ESR is arguably one of the most significant "legacy" browsers. Scroll down to Firefox Updates
Mozilla and security experts strongly advise using old versions of Firefox for general web browsing. They contain known, unpatched security vulnerabilities that can be easily exploited, putting your personal data, passwords, and computer at severe risk. These versions should only be used for their specific, narrow purpose and ideally in a secure, isolated environment like a virtual machine (VM) or an offline computer.
If you want, I can:
Launch the Profile Manager before opening the browser by running firefox.exe -P via the command line.
Use these versions strictly inside an isolated virtual machine if possible.