But many (I'd put my money on "most") users' first reaction isn't to issue a reload with the extension disabled. A lot of users aren't even aware of what extensions they have installed, and their first reaction is to file a bug report to the website.

It would be nice if there was some way to prevent users from reporting bugs if they have extensions modifying the website in certain ways, or at least warn them to try disabling their extensions first. I wouldn't even mind a whitelist for certain well-behaved ad blockers, but certain extensions are well known for being bad (many extensions _inject_ ads, which is a recipe for website breakage).