Make sure our updates are dealing with SSE requirement properly

https://bugzilla.mozilla.org/show_bug.cgi?id=1271761 landed on ESR45 and it is very likely that Firefox won't work on machines without SSE support anymore in the next ESR (52). We should make sure we handle this properly with our updater. We want to be sure users without SSE support won't get an update then, for instance.