I have little doubt that this'll be one of those stupid questions that five more minutes of searching could've solved. How many minutes did I spend searching? Doesn't matter; five more would've done ...
Gentoo-current. KDE 3.1.<BR><BR>Right-click on the "K". Menu Editor. Internet. New Item. Item name: Mozilla Firebird. Command: /usr/bin/MozillaFirdbird. Apply. K menu -> Internet -> Mozilla Firebird.