Firefox Sync "synchronizes" the data types the user selects on the connected devices.
If you select Bookmarks in Sync settings, your Bookmarks on that device will be synchronized with those on the Sync server. If Bookmarks isn't selected on a particular device, Bookmarks on that device won't be part of each Sync session. If you only select Tabs to be synchronized, your History won't be Sync'd - only what is selected on a device will be part of each Sync session.

to the-edmeister,

you did not read the whole question.

Consider this part: "Will the sync import all settings and merge them or will the settings remain separate somehow"

I too would like to know what really happens on the two different browsers when sync is performed. Is the data merged so that both browsers have a super-set? Or is the first imported to the other? And if so, does the second end up with a total replacement, or a merged set.

Sorry, but I did answer both questions.

synchronize means "make the same" - save separately isn't a "sync".

So, of course the data is merged on the server so that all connected devices have the same data. The only exception is browsing history, that isn't completely synchronized, only the most recent history is sent to the server to be shared with the other devices.

Thanks for the reply. It is encouraging to see such timely responses!

I must be old-school ... you know, mainframe days... ;)

To me synchronize does not necessarily imply merge both into a superset.

Sometimes synchronize means: make one look like the other. (See refs at wikipedia or other online definitions. I only point this out to explain how it is that I do not automatically assume the same process function for the word that Mozilla does. And having worked with user documentation for years, it seems that clarifying of assumed terms is important.)

Though I am not sure if any authors of the Firefox help pages ever read here, I would wish that they would include just this extra little tidbit - that "synchronize" in Firefox means creating a superset of all data, and then making both look like the superset.

Would have saved me a lot of time searching and worrying about what will actually happen. Sigh.

The one other thing, which I will probably have to experiment with, regarding bookmark synchronizing:

What does it do with two similar but not exact bookmarks.

I am guessing that it will try to match on URL address, not text label. So i wonder what it will do if I have same URL but with slightly different text name label, which one does it pick? Or perhaps it will keep both, if its match criteria is both of URL and text name label.