Edit: Just checked and my work bookmarks appear to be all there. I did a fresh backup through the Library tool just in case. Hope you get your issue sorted.
This seems to be a bug, affecting big sized folders ( Folders with subfolders and lots of Bookmarks ), these are the folders that got Bookmarks removed from them ( in my case they were political which spooked me a bit )...
I should join Mozilla's forums and talk about this, it'll be noticed there by the Devs, but.... yeah.... Sync is not enough to save your Bookmarks, and you should always keep a local copy... Luckily I did .. 😮💨
I meant if they were mostly in one folder, if the list is so long that when you open the folder, the bookmarks continue past the bottom of the screen so you'd have to scroll to reach the bottom. One of my folders is like that 😅👀
Yeah, and a lot of research gone, and a lot of work to get them organized, I still have most of them in a local backup... 😮💨
the bookmarks continue past the bottom of the screen
Yeah, lol... In my case you have to scroll down to see other subfolders, which contain more subfolders and finally you get a list of Bookmarks that < again > goes off the screen..