Sharing something easily is one thing, but they seem to be planning to provide a newsfeed/wall with this. That'd be a big distraction that I hope they keep away...
For people spending their days on Facebook it might be an improvement. It does sound like a huge addon though and I agree that it'd probably be best to make most of that non-default.
The problem is, how keenly will the various services let something like Firefox take their newsfeed? This is exactly what Twitter for example is trying to prohibit with their ToS. Just sharing is a lot more durable.