I wish there were a Firefox extension to handle manpages in a similar way to Konqueror. Instead, I use man2html. I setup a Smart Keyword so that typing man firefox for example retrieves the manpage for Firefox.
Unfortunately I feel its output is not as pleasing as Konqueror's. As a stopgap measure, I use the Greasemonkey Firefox extension to add some CSS to make the pages more to my liking.