The tab is linked to the page, so why should it be at the very top of the screen, not the page?
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. Thanks Mozilla!!! 
Hmm with only 2GB RAM the problem lies here unfortunately especially when doing memory hungry tasks.
2gb memory is fine.
got a problem with fonts since installing FF4. Under FF3.6 the fonts were clean and sharp, now they just look horizontally stretched, but this is on on the page, all other fonts are fine