Sorry, that isn't a feature for Sync services. It's all or nothing with regards to bookmarks; either ON or OFF for the various data types that Sync works with.

Yes, it is possible to export a selection of bookmarks from Firefox, but the problem is when importing those bookmarks. The import bookmarks feature appends exiting bookmarks, so when doing that multiple times to get recently saved bookmarks you would end up with an ever increasing number of duplicate bookmarks each time you do an import via HTML format bookmarks.

Support article here for Import (and Export) of bookmarks in Firefox.
https://support.mozilla.org/en-US/kb/import-bookmarks-html-file

That said, you can run multiple Firefox Profiles on each PC and in the same Windows Logon User Account quite easily; like two Profiles, with one for Work and the other for "Home". And Sync can be used, with 2 Firefox Accounts / Sync accounts like for Work and "Home" Profiles. Sync works to synchronize Firefox user data between the Profile, not the overall Firefox program installation.

https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
And at the bottom make sure you see the Working with profiles section.

Does get to be more complicated with iOS devices (and Android devices); I am not well versed on the "mobile device OS's, as I don't use Firefox on any myself.

Note that this means you need to use a separate Sync account for the work computer that only has the bookmarks for work and not the other home related bookmarks. You will have to decide for yourself if you want to add new bookmarks to the work profile when working at home with this profile. Note that you can run multiple profiles at the same time and you may want to add a theme with a different background color for the user interface to avoid confusion.

very helpful. I will have to ponder how I want to manage this. A separate work account might simplest.

I tried this, and at first it seemed to be OK, but now I'm getting a message when I login to the work computer that says 'using an older version of FF may corrupt your profile' and offers only 'exit' or 'create new profile'.

Home computer is Mac/Mojave, work computer is Windows 10 PC.

I've long used beta channel for updates on Mac, but was afraid to use the less stable version on work PC.

Is beta vs regular release channel the problem, or Mac vs PC versions, or both?

(ignore, wrong thread)