Firefox 3.6.19 seems to be incompatible with pixel perfect. When I first enable it, it seems to work for a minute, then when I try to use firebug, selected elements start flickering. Then I can't use any other tabs on the firebug panel at all (when I click on them nothing happens). I tried unchecking the checkmarks next to pixel perfect or other panels and that doesn't work either.
i have the same problem. when PP is enabled i cant use firebug anymore. The only thing that helps is to restart firefox. OSX lion + FF 3.6.23
firebug doesn't work after enabling pixelperfect in Firefox 7 either. Not only that, once pixelperfect enabled, Firebug's other panels don't work AT ALL, even when restarting the browser. I had to uninstall firebug and reinstall it.
Same problems with Firefox 8.0.1 for Windows (XP Pro 32bit) and Pixel Perfect 1.7.1
Firebug panels are disabled and no overlay image displayed.
Firebug features becames totally unavailable when pixel perfect is enabled (pixel perfect features too!!).
It happens when you have pixelperfect open on two tabs or more. Very annoying.
Same problem. FF 10.0.2 && FB 1.10.0a5. After restart FF all work.