I too see absolutely no point in this. For one, you're -always- going to be switching between your "browser" and mIRC, even if it WAS contained in a tab, you'd -still- have to change tabs to go back to what you were browsing.

I believe firefox already has an addon for IRCing. https://addons.mozilla.org/extensions/moreinfo.php?id=16&vid=999

Sure, it's not mIRC. But nevertheless, it's still IRC in a tab.

Enjoy.