Only way to disable this is to open about:config and change some value. Why this has no dismiss button?
There is couple more settings that are on by default and i hate those; but mostly those are subjective. However who wants 80px long “SIGN IN SO WE STORE YOUR BOOKMARKS, HISTORY IN OUR SERVERS” stuff on their screen?
It’s pretty good yes, but it also has that sign in to sync banner by default.
That’s weird, I’ve never seen it