The two little things that annoyed me most:
When inspecting an element, the element is per default collapsed (i.e. it's children are not shown). Often, I want to see the children as well - one more unnecessary click. This may be a good design decision if the tools are running on a laptop screen inside the main browser window, but I'm using two monitors and the tools take a whole screen.
Related, my main monitor has a terrible (=no) contrast between white and light gray if viewed from some angles. Often, if I inspect an element, I'm missing the highlight (light gray on white)... Yep, I should probably play with the monitor settings, although FF seems to be the only tool I have this problem with.
These are obviously not big issues and I don't miss the Chrome tools too much, so I'm sticking with FF. Keep up the good work!