Don't get me wrong: I love Web Dev; if I didn't love it, then like most add-ons in the entire world, I wouldn't use it. It does things Firefox's built-in Web Dev tools can't do and sits up there in my toolbar begging me through my peripheral vision to click on any of its many tools so convincingly that I have a hard time not using it just to use it. I don't think I've found all the tools it has yet and that's with steady, regular use going back at least five years.
The Dev in Web Dev either deliberately broke or else accidentally lost right-click functionality back in '11 or '12 and never bothered to fix it. It's on his list, of course; so is making pigs fly, if you look hard enough (alright, I may be kidding about that, but for all the difference it makes). Luckily I'm sorta handy with a keyboard - and the keyboard functionality, with some exceptions, still works - so it's Ctrl+A, Ctrl+C, Ctrl+V, Ctrl+X, Ctrl+Z and Ctrl+Y all the way. That's bad enough, OK?
On Nightly it's not just all-keyboard-all-the-time FTW, but - but! Web Dev sometimes loses focus so that when you're in the CSS live edit console and hit, say, Ctrl+A, you wind up selecting all the text on the page instead of in the console. It's a seemingly random thing so you never know when it will happen nor what to do to prevent it (fwiw, it seems like a rather exotic mutation of this bug, which he thought he had fixed). Figuring out how to fix it yourself is even harder because when you lose console focus the CSS is uneditable, so when you go to hit say, the backspace key, nothing happens. I stumbled on the answer entirely by accident.
You can easily "fix" the freeze by highlighting and deleting any CSS in the console. It can be any amount of CSS - one character, the entire style sheet or any amount of code in between. Once you delete something, anything, the console "wakes up" and works again. So it's highlight, delete and Ctrl+Z (assuming you didn't want to delete anything) then proceed as usual. Until the next problem, which you'll probably run into shortly.
The console freeze is a strong clue to the next problem, and usually shows up within minutes of you "fixing" the freeze by deleting something: the "live" in live edit stops working. You can still use the console - it's not frozen - the damn page is. So say you're changing margins, padding and backgrounds furiously only to notice many seconds or minutes later that nothing's happening on the page - this is because somehow the live link between the console and page has been broken. You'll have to reload the page to fix it, but reloading will often loop you right back to the first issue in which the console freezes harder than a rock again.
After enduring many hours of this I've decided if the Dev in Web Dev knows about this (but doesn't fix it) then there's a good chance he's not just time- and cash-strapped but is also perhaps a sadist. It's made editing feel like plunging into the seventh circle of hell (yes, in hell we'll have nothing but really crappy editing tools...kind of goes with the overall atmosphere down there, I guess).