I've been using 2.0 for about a month now and so far it has been as stable as the previous version for me.
I don't like the keyboard shortcuts in Firefox since they so often conflict with the Web sites I may be browsing, but while Alt-S may be new it has been enough of a problem that I just haven't used keyboard shortcuts at all for a long time. I can't remember.
However, if you don't want the History menu option (and it isn't something I would ever use, you can install the
MenuEditor Add On and turn it off. This will, I believe, make Alt-S work in your preferred way again.