Download Firefox 12-51 52 Esr May 2026

This is expected. Modern HTTPS standards (TLS 1.3) and certificate authorities often reject Firefox 12-51. You can try enabling older TLS versions in about:config (security.tls.version.enable-deprecated), but this is a security risk.

Do not use these versions for everyday browsing – they have unpatched critical security vulnerabilities. Use them only for:

If you are downloading for a corporate environment, avoid standard version 52.0. You want 52.x.x ESR. Download Firefox 12-51 52 Esr

The ESR (Extended Support Release) is designed for organizations. While standard Firefox 52 received security updates only until September 2017, Firefox 52 ESR received security updates until September 2018. For Windows XP users, Mozilla extended this specifically to 52.9.0 ESR.

Critical note for 52 ESR users: If you install Firefox 52 ESR, you must immediately disable automatic updates. Otherwise, it will auto-upgrade to Firefox 60 ESR (which drops NPAPI support and will break your legacy plugins). This is expected

How to disable updates in 52 ESR:

Mozilla officially maintains an FTP server at archive.mozilla.org. This is the safest source (No viruses, no fake installers). Do not use these versions for everyday browsing

Navigate to: https://archive.mozilla.org/pub/firefox/releases/

Select your language (e.g., en-US). Download the installer file ending in .exe (for Windows) or .dmg (for Mac).

Direct Download Examples (for reference):