Just a note that this happened to me, maybe this isn't the correct place to talk about it, but I found no other... I keep my browser (of course) and many other programs on my 4GB cruzer, I often times have family and friends who have issues with their own computers and I therefore carry many adware/spyware detection programs and whatever the best free antivirus program I can find on it. Well I recently wiped McAfee off my Mom's computer and installed AVG antivirus in it's place, and at some point in all that I was running and fixing, I ran my portable firefox. Well apparently this allowed the AVG to install it's browser bar and low and behold, the next time I went to run portable firefox, my theme went to default, and all of my add-ons were non-operational. It wasn't until I found the AVG bar items at the top of my list of add-ons that I realized what was going on. I shut the 2 items down, and everything was back to normal. The odd part is, I never told it to install onto my Firefox. My mom's computer uses IE (ugh, she's 67 years old, I cant make her change browsers now!).