Going back : unfortunately 56.0.2 and below is no longer safe to use for every day use do to secuity issues, but 52.5.2 ESR is. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ Note : Legacy Extensions will be deleted or removed in any version update after May 2018.

You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Please let us know if this solved your issue or if need further assistance.

First, Type about:preferences#advanced<enter> in the address bar. Under Advanced, Select Update.

[v56+] Type about:preferences#general<enter> in the address bar. Select Update.

Select Never Check For Updates.

Also turn off Use a background service to install updates

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

Your Firefox is identifying itself as version 45 which is rather ancient now. Is that correct??

The following was written for Windows, but I think if you change "Windows Explorer" to "Finder" in your mind, and Ctrl+c/Ctrl+v/Ctrl+a to use the Command key, the steps would be the same: I did a Reset of Firefox - How do i get add my 'Old firefox data' back?