Sync to a new browser always merges the default configuration without asking. The Sync does not sync the 'limit to designated sites' option, so you have to manually apply that to all the categories (while you clean out the merged in default configuration).
Management of the categories is woefully sub-par; how is there no way to manually add domains or wildcard domains to a category? Try keeping a service like Google in a 'limited' category and watch the SSO explode every time you go to maps dot google dot com because the browser doesn't stay on the auth redirect long enough to add it to the container though the UI.
It also breaks the firefox profiler, as the profiler can't load profiles from outside the category.
None of this bothered me when this feature was new, but it's been years. I wish I could recommend this and use it in earnest.
