If you really want an extension that requires that, and if it has a repo, you could vet the code a bit (it's JavaScript, so somewhat accessible), and load it as

If you really want an extension that requires that, and if it has a repo, you could vet the code a bit (it's JavaScript, so somewhat accessible), and load it as an extension from a file after packaging it up. Alternatively, you can install it, look in your profile dir until you find that extension, and look through all the code it's using, and turn off automatically update extensions in Firefox when you're happy you want to keep it. People can say what they will about the great extension convergence where Firefox switched to Chrome style extensions, but having everything just be JavaScript that you can easily review yourself is pretty nice.