Recent changes in Firefox makes bookmark and password cloud apps a pain to set up, with obligatory fiddling in about:config and removed config on upgrade or else.
An alternative would be to use Firefox Sync. But I am not using only Firefox and I do not like the notion of using a solution tied to one browser. Plus, installing Firefox Sync on your own software is, last time I checked, neither properly documented or made to use existing cloud authentication.
Password-wise, I switched over KeePassXC. I am not documenting my setup now because it still experimental and I know password managers are subject to hostile hacks. So I’d would not encourage people to use an half-baked setup.
Bookmark-wise, I tried a few things. You can fiddle around places.sqlite but it changes so much that any sync of this file on a cloud is bound to generate lot of useless trafic in best scenario, conflicts otherwise.
However, Firefox save automatically backups of bookmarks in .json (simingly compressed with lz4, though package liblz4-tool in Devuan/Debian is not helpful is decompressing them) in .mozilla/firefox/random.default/bookmarkbackups/ and this directory can easily be synced.
Then, on another client, when you open the bookmarks window, you are presented with the option to load such backups, telling how many entries are within each backup. The process is half automated – far from perfect but much less broken than anything I tried so far.
I am sure it could be possible to improve this to a fully automated solution (adding new entries is easy to handle, noticing removal a bit less, it would require some database). I’d be interested in any alternative.