Since this version I also have the same trouble as many others reported here:
WebRep works all time fine in the toolbar of FF4. If you search with Google the WebRep symbol on the search results are allways grey while the symbol in the tool bar works ok.
If you than refresh the page WebRep on search results is indicating normal. If you search after that a different thing the whole procedure starts again!!!
There is no exception to this rule whatever you do. Even a new installation will not help.