After Firefox is close for a few hours, when I reopen it, it reverts back to an earlier state. How do I prevent this??

I recently downloaded the newest version of Firefox, but ever since then, whenever I close out Firefox for the night, and reopen it the next day, Firefox has taken off my preferred theme, and reverted it back to the original non-theme. It also reverts my homepage to a Firefox "search engine", and also opens up a second tab inviting me to take a tour of the new Firefox. I want to be able to re-launch Firefox after a night or longer of being closed...WITHOUT having Firefox revert to the "search engine" for the homepage, and without putting up that "take a tour" tab. My preferred homepage is https://www.facebook.com, but it reverts back to the "Firefox Search Engine" when I re-launch Firefox after several hours of being closed. How do I put my preferred theme back on my Firefox browser, and KEEP my homepage at https://www.facebook.com (and NOT have it revert to the "firefox search engine")??