. Users remaining on this legacy OS face significant security risks as this version ceased receiving critical security updates in October 2021. Technical Findings Last Compatible Version
Look for the folder named (the final 78 ESR). If you want the absolute last version for 10.10.5, choose: firefox download for mac 10105 upd
, you may have noticed that downloading the "latest" version of Firefox from the main Mozilla website If you want the absolute last version for 10
: Click the link above and select the .dmg file. Open the Installer : Double-click the downloaded file. Mozilla may remove older builds from archives, but
Last verified for compatibility: May 2026. Mozilla may remove older builds from archives, but the paths mentioned remain valid as of this writing. For commentary on legacy Mac browsers, check the r/firefox and r/macos subreddits.
Navigate to the official Mozilla FTP archive or the Mozilla Support page for legacy systems . Download the file named Firefox 78.15.0esr.dmg . : Open the downloaded .dmg file from your Downloads folder. Drag the Firefox icon into your Applications folder.