Now I've got plenty of tech illiterate friends, and they've asked me many questions over the years, but never did it have anything to do with browser settings not loading pictures or javascript.
In fact, it's the one thing people tend not to mess with. They'll do tons of weird software, they'll even do regedits from a misinformed guide, but touching browser settings? I don't know about you, but none of my friends ever did.
So what's the problem here? Don't see one. What's the solution if there was a problem? Create a 'dev-mode' button, give the user a warning they shouldn't use it unless they're software developers, and put your tricky settings behind that wall.
The solution doesn't seem to me to require people to install add-ons for what is basic functionality to a decent amount of people, especially not in an addon store with lots of third-party crap that might work now, but doesn't work in combo with another add-on, or stops working after the browser updates and the add-on dev moved on to other things.