I installed Cooliris in FF 18.104.22.168 - it's pretty neat, no denying that.
After a few hours of use my system started to slow way down - I checked memory usage and saw 360 megs for Firefox! A few open/close cycles showed that with Cooliris installed, Firefox was using about 200 megs more RAM at startup than without it.
Without Cooliris, it's very unusual for FF to go over 125 megs on my system, even after a full day of use. I decided that, for me, it's almost as convenient to just open a new tab to take a quick look at a site, so I got rid of Cooliris.