I'd like to share my bookmarks, not passwords, across devices. Seems straightforward for my own PC, laptop, phone. We hot-desk at work, each with our own Windows login. When I use FF there, I have my own set of bookmarks so assume it's specific to my login. So if I sync to that computer, will FF just sync my own bookmarks, or might it combine those from other users? Or might my bookmarks be syncd to someone else's FF too and clutter them up?
And while I'm here - can I set it to sync bookmarks but not passwords?
Firefox Profiles are specific to the Operative System user. If you login with other user, you will have a different Firefox profile in place.
That said, Firefox Sync is configured on a profile basis. So no problem at all in the configuration you are looking for.
Regarding Passwords. Once you have set up your account, you can go to the Sync Tab in the Preferences window and you will see a list of things that you can synchronize. Uncheck those ones that you don't wan to synchronize (including passwords).