I am having the same problem. I am using Windows XP and Firefox 4. The strange thing is, I had the WebRep extension on for a month, and iGoogle worked fine all that time. Today it broke. Nothing has changed in my system, that I know of. I found the info about WebRep, and disabling it definitely solves the problem. I like the WebRep extension, and I would like to be able to use it. Any new info on this?
Thanks