When I click onto the Firefox 54 icon after installation, the Firefox menu bar at the top of the computer greys out and nothing else happens. Since I installed the earlier version of Firefox it has been working for me even though it updated itself to the latest version. Read this answer in context Many have reported problems with v54.
That is, the Firefox browser does not start, nothing happens. But I'll keep these tips in mind should there be an issue in the future. For now, consider this; Install Older Version Of Firefox Be sure to read everything here.
Firefox Extended Support Release (ESR) 45 will continue to support OS X 10.6, 10.7, and 10.8 until mid-2017, but this ESR release will be the last that supports them.
All three of these versions are no longer supported by Apple.
''' Trash''' the current Firefox application to do a clean install. see also: [https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac#firefox:mac:fx43 How to download and install Firefox on Mac] thank you If there a problem with updating or with the permissions then best is to download the full version and trash the currently installed version to do a clean install of the new version.
Download a new copy of the Firefox application and save the disk image file to the desktop Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you uninstall and (re)install or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.
Mozilla will end support for Firefox on OS X 10.6, 10.7, and 10.8 in August, 2016.