Sorry Dani... still unable to reproduce any crash-like behaviour for you. Tried following some links from your twitter as mentioed above.
The new ad-hover-background is much more responsive in FF than the striped one was. I did notice that at one point it stopped appearing when hovering over the right hand ad - but then I scrolled and it came back (haven't been able to reproduce, and no errors reported in js console)... weird.