Type about:config<enter> in the address bar. If a warning screen comes up, press the Be Careful button. At the top of the screen is a search bar. Type browser.startup.homepage.

Click on this to edit. Look for |about:preferences#general or |about:preferences and remove it.

I've tried that. After I close Firefox it clears my changes and reverts to https://www.google.com/?gws_rd=ssl|about:preferences

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Note that you can drag the globe/padlock at the left end of the location/address bar to the toolbar Home button to set a single page as the home page.

Thanks cor-el. Tried it, but it didn't resolve my issue.

Did you check for issues with the preferences?

You can check for problems with preferences.

Delete possible user.js and numbered prefs-##.js files and rename/remove the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in current Firefox releases.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

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