The theories of GBrowser seem to be endless of late. The hiring of two senior people from Mosiac has been heralded as the sign of either Google buying Mosiac or them developing their own browser.
Little has been written about the possibility of them just wanting to better adapt the Google toolbar to FireFox which would be my guess.
With MSN about to enter the PPC and search wars, I would not be surprised to find it harder to add the Google toolbar to the Explorer browser. Or at least not the full version that can be used now.