Just installed Firebug 1.5 (after using 1.4.5 for a long time) and first thing I noticed was that the inspect element did not work correctly. After hovering on an element, the html tab did not show (or expand to) the element. Then I noticed that even manually expanding an element (by clicking on the + symbol) also did not work after 3 or 4 level deep.
After some googling, I finally out it was due to FireQuery. I was using version 0.3 and after updating to 0.5, all issues fixed.
I would also like to use the opportunity to thank the Firebug team and ofcourse FireQuery for their great tools!