This happened once before, and today again: clicked on Firefox icon, and I got Google’s search page. (Our home page is Yahoo) I went to Tools - Options - Main and it showed Google as the home page; changed it to Yahoo. But…all my bookmarks are gone!! I did a search and found an old list in the recycle bin (deleted five months ago) which I’ve imported, but it doesn’t have bookmarks from the past few months. Any idea what’s going on here?
It has happened to me too. It seems to have been when my machine crashed. Here is a link about recovery and prevention.
I got a new version of Firefox yesterday, and it had lost some of my bookmarks (but not all) and changed my homepage. My homepage had been a 5-tab page, including 4 of the pages that were among my lost bookmarks, so I had to spend a bit of time re-locating those lost pages, but I managed to do it. I should really keep a list of my important bookmarks in a document outside the Firefox environment 
Firefox does five backups. Try one of them.
Here is one link. I can’t find the threads I’ve answered on this before, so I’m posting this link. Many sites have the information you need, now that you know there are backups. You need to do this now. Waiting may lose all the old backups to time.
Sorry I haven’t responded sooner; I’m not getting email notifications about replies. Glad to know it’s not just me. I’ll follow-up on your suggestions. Thanks.