I kept my home page set to what I want by setting it up the way I like it, then copying the setting from prefs.js to a user.js file which is saved in the same directory as prefs.js (the profile). When Firefox is upgraded to a new major version, I launch it, close it, then launch again, and my home page is restored.

browser.startup.homepage - the setting to be copied

See these articles for some suggestions:

• https://support.mozilla.com/kb/Firefox+has+just+updated+tab+shows+each+time+you+start+Firefox
• https://support.mozilla.com/kb/How+to+set+the+home+page - Firefox supports multiple home pages separated by '|' symbols
• http://kb.mozillazine.org/Preferences_not_saved