I'm used to developing using both Chrome and Firefox. My little problem with Firefox DevTool is that I like to have this windows separated from the main window, where the page is. Yes, I do that. But I must say that Google Chrome version is less confused in that, because of how it shows the DevTool icon in the taskbar.
The main difference is that Firefox shows it like another window in the same icon program, while Chrome create another icon program separated in the taskbar, so I can easily know which one is the icon with the page and which on which the DevTools.
I know that it could be some stupid, but I'd rather like the way Chrome implemented this, and it would be a great little detail in the Firefox for me.
I hope that you can understand what I'm writing (English is not my mother tongue)
P.S. I attach a screenshot where you can see how I have this window and the DevTool with Firefox (all joined in the same icon, same space) and a window with Chrome and the DevTool separated in another icon.