Mozilla: no, we can't let you load extensions from your own machine that you control, that would lead to security problems due to outdated extensions!
Also Mozilla: here's an update for one of your extensions! btw it has malware in it because its author's account got compromised. also we're not going to let you roll back to the previous version that doesn't have malware, because being on the latest version is super important for security!!!
https://github.com/brookhong/Surfingkeys/issues/1796