Since Firefox 45 ESR has been retired, there is no currently up-to-date Firefox available for your Mac. See: [[Firefox support has ended for Mac OS X 10.6, 10.7 and 10.8]]. If you want to use the last supported version, you can get it from the following folder (click the "locale" code for your country and language, for example, English language versions start with en): http://archive.mozilla.org/pub/firefox/releases/45.9.0esr/mac/ As always, bear in mind that security vulnerabilities have been publicly disclosed for older versions of Firefox, which puts older Firefox versions at greater risk for attack/compromise. More info on .dmg files: [[How to download and install Firefox on Mac]]

But I also should mention that reinstalling is not a "cure all" for Firefox crashes. Please see this article for suggestions on troubleshooting those: [[Firefox crashes - Troubleshoot, prevent and get help fixing crashes]].