FF is under rapid development. They switched the way they handle bookmarks
etc. switching from an xml file to a database. 10.10 probable used the old
way, but newer versions use the newer method. So if you have your bookmarks
in the old bookmarks file and a newer version of FF is looking for them in
an sql database them having the bookmarks file is of no use.

The way around the problem is to export the bookmarks then to import them
into the new version of FF.

I am not sure if this is your problem, but it sounds similar to one that I
encountered awhile back.