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.
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.
I have used it more or less exclusively for a couple of months and it works nicely everywhere except for some pages with JS developers who manage to write "your browser is not supported" for anything but Chrome.
You can use the Firefox Developer Edition, which will continue to support the xpinstall.signatures.required preference allowing unsigned extensions.
Developer edition is "Aurora". Aurora is alpha. Alphas have more bugs. It's not reasonable to tell me to use an alpha.
Excuse my ignorance, but is this official? I use FF Dev edition as my primary browser and it is very stable for me.
Context, if it helps: I am a web dev most of the time, and my browser usage is almost always >100 tabs or so. More than half of those have the devtools open all the time (each of which basically count as another instance of Firefox). My machine is pretty modest (i5, dual core, 8gigs RAM). I don't use many extensions though. Only a lightweight custom theme and greasemonkey + lots of custom userscripts. Reason I use dev edition is because it has more devtools goodies and ES6 features. Nothing related to extension development.
> When they bump the version number Nightly turns into Aurora turns into Beta turns into Release.
Not exactly. I guess you intentionally (over-)simplified that? Firefox actually follows trainspotting for their different release channels: https://hacks.mozilla.org/2015/04/trainspotting-firefox-37-d...
Aurora is alpha, but FWIW, I've been using Nightly as my main browser for over 4 years now without ever losing data, so Aurora should be more than fine.
It crashed on me twice in as many hours. I'm pretty hard on browsers since I typically have 200+ tabs loaded. That never happens with final release versions.
I am not an extension developer but it's a rare month when I don't find myself popping open an .xpi to make changes to the JS and HTML for personal aesthetics; or bugs only I have. Temporarily loading extensions is not a solution. They say they'll be producing an "unbranded" non-walled garden version that for technical users but no such build has been revealed yet. And if they do make it the unbranded version won't be in my OS repos.
This walled garden, the addition of Adobe EME/DRM, the bundling of "Pocket", and the incoming drop of XUL based extensions are too much.