This is doable on linux/unix through an NSS plugin (and has been linked to in this discussion), but the vast majority of Firefox users are on Windows (and a minority on Android) where this cannot be done as easily.
For the users, 99% of whom live in the self-updating browser these days, this is much better than waiting for an OS patch that they may or may not know how to install.
For the users, 99% of whom live in the self-updating browser these days, this is much better than waiting for an OS patch that they may or may not know how to install.