It is very good. One problem, I always have to click twice to get it to open. When I first click I get a small white empty "label" (where the loading bar is supposed to appear) and then I click somewhere else to make the empty "label" go away and then click again and it works. I wonder why it does that.

EDIT: After restarting FF, it seems to have fixed it. So you can discard the "bug report" and just keep the 5 stars :)