Unfortunately the new hardware acceleration feature in Firefox 4 Beta 5 seems to have a bad impact on font rendering. There is already a fair amount of negative feedback and users turning this feature off.
Here are some examples with hardware acceleration on (left) and off (right)<p><a href="http://a.imageshack.us/img231/5900/firefox42.png" rel="nofollow">http://a.imageshack.us/img231/5900/firefox42.png</a><p>Obviously the header text here is completely messed up. But the normal text is horrible too. Look at the N and the D at the beginning of the first posts - previously nice and sharp 1 pixel lines, now 2 pixels. The T on The on the third post runs into the h, rather than having a gap.
The text was previously sharp and crisp, now it looks blurry.<p><a href="http://a.imageshack.us/img291/9493/firefoxbeforeafter.png" rel="nofollow">http://a.imageshack.us/img291/9493/firefoxbeforeafter.png</a><p>Look at 'sebastianmarshall.com' on line 4 - it's so much more compressed. In fact, before it is 139px wide, with acceleration it is only 132px wide: it's not just the look, it's actually changing the dimensions of the text!