It is. And it's done because Firefox doesn't expose the right hooks and isn't interested in exposing them. They obviously know what's happening already. From

It is. And it's done because Firefox doesn't expose the right hooks and isn't interested in exposing them. They obviously know what's happening already. From the addon's point of view, the option is do it via regular expressions or not at all; it turns out the most users don't actually care how things get done.