More info. Firefox starts (using SAME profile as always), but bookmarks are empty? In the active profile, there's folder "bookmarkbackups." Can restore latest copy. In bookmarks library > Restore > choose a json file from bookmarkbackups (any recently used profile where "full" set of bookmarks were used). If done a bookmark BU to HTML file, that's for the "import bookmarks from html file" (or if did a recent system or just Fx profile BU, can recover them from there.).