I use direct links on the Firefox bookmarks toolbar for sites I use frequently, like timesheets. I use folders for items I use less frequently, but still often.

I have a Current folder for sites I want to read, that I try to purge periodically. And I've tried Firefox tags which seems to be the ideal way of keeping bookmarks, but rarely search by tag so not sure it's worth it.

Firefox bookmarks sync is nice to us between browsers, but i end up having both personal bookmarks and work bookmarks. Ideally it would be good to keep them separate but yet to find a clean & easy solution.