"Linux offers Ctrl-C/Ctrl-V paste just like Windows and Mac
(Cmd-C/Cmd-V on Mac). But it also has a second way of copying and
pasting: anything you highlight with the mouse is automatically
copied into X's "Primary" selection buffer -- which doesn't change
whatever you might have copied with Ctrl-C -- and you can paste it
pretty much anywhere by clicking the middle mouse button. If you're
on a laptop and don't have a middle button, try clicking the left
and right buttons together. If you've been using Linux for a while,
you probably already knew all that.
"What a lot of people may not know is that Firefox, and most
other Linux browsers, give you a shortcut for pasting URLs. Instead
of the three step process of clearing the URLbar, middlemouse
pasting, and hitting Return, just click your middle button with the
mouse somewhere in the content area -- the main part of the browser
window. Firefox will go straight to whatever URL you've selected
with the mouse."