If you find yourself copying and pasting URLs around, this is one a must.

CoLT extends the context menu on links, allowing you to easily copy the link text (the text that is highlighted as a link) and also the URL and text in a variety of formats. If you find yourself needing to ‘borrow’ someone else’s definition (for free software, for example) then copying the two pieces of information at once saves time and effort.

Get it here: https://addons.mozilla.org/en-US/firefox/addon/1812