They'll be en-US only, though, so if you want a non-English interface, you're out of luck.
As far as I can tell, side loaded extensions require a full, non-automated, review http://i.imgur.com/r070Grv.png and it wouldn't surprise me if side-loaded extensions were the worst offenders.
Upon discovering a malicious extension, Mozilla could look through all extensions they've signed and blacklist (https://addons.mozilla.org/en-US/firefox/blocked/) all extensions with a similar signature similar to how some anti-malware databases work.
There is probably not all that much stopping you from writing a malicious extension that passes the AMO automated review (example: https://addons.mozilla.org/en-US/firefox/blocked/i1058), but the cost for malware writers is going to be significantly higher since it will be far easier for Mozilla to shut them down via their blacklists.
1) Creating an AMO account and running the command line "jpm sign" tool yourself. This requires a bit of overhead per each new addon you want to make modifications to, but the actual signing of unlisted addons (which is entirely automated) had been fast and mostly painless in my experience.
2) Using Firefox Aurora/Developer Edition as your main browser and relying on its automatic update mechanism.