I'm presently running Firefox 3.6.8 on Ubuntu 9.04. My Firefox extensions include Ubuntu Firefox Modifications 0.9rc2. I've upgraded Firefox on this install a few times; as far as I can recall, some version of this extension was present when I initially installed Ubuntu 9.04. I have disabled it, mostly because I didn't know what it provided me, nor was I able to find out when I tried a bit.
What does the extension do?