I used to agree with you until Firefox 25 or so. In fact, I always tested mainly in FF (as that is my main browser) but I'd switch to chrome when I needed any sort of debugging or inspecting more complicated than reading the console.

But in the past couple revisions, I've found myself going to Chrome less and less often. Hardly ever any more with 27, and never first. Mozilla is making constant improvements and I'm quite happy with them. The debugger seems very solid to me inspector is just as good as chrome. The Chrome profiler's flame-maps are pretty awesome though.