Back in the mists of time I wrote some code to make nightly testers’ lives easier by giving them a simple preference to flip if they wanted to be able to install and use incompatible extensions. It’s been more than three years since then and the use of this preference has grown beyond its original use. It is now something recommended to regular users everywhere from forums to comments in news articles as a way to use their extensions in the new major Firefox releases.

Don’t get me wrong, letting users upgrade sooner than they otherwise might is a good thing, but the preference is a dangerous beast. It is pretty simple for a user to set the preference and then forget about it leaving them able to install incompatible extensions that break their Firefox without realising it. This costs Mozilla time as well since we get quite a number of bug and crash reports to look at that turn out to be caused by extensions that are dutifully marked incompatible with the user’s Firefox.

We’ve been mulling over ways to change this for a while but now we’ve actually gone and done