Previously, I could write an addon for personal usage packed as something.xpi and I clicked on it to install it.
After a while, mozilla introduced xpinstall.signatures.required which you could still get around it.
However, it did not stop stabbing developers who are interested to have a personal addon isolated from the world. Today, only web extensions are working and my XUL based addon is thrown away. The tutorials only talk about temporary installation of a web extension while I want my one runs on firefox forever.
Beside whether I can use web extension to write into files or create a GUI in an independent page, I have a bigger challenge:
How can I install a local web extension permanently without creating a Mozilla account for personal usage?
Navigate to the folder where your extension is located. You can build it in the usual way using web-ext:
web-ext build
You can install this ZIP file permanently in Firefox by going to about:addons and dragging this file into the tab.
In order for this to work, you need to set xpinstall.signatures.required to false in about:config (works only for Nightly and maybe Developer Edition).
You need a "blueish" Firefox -- Developer Edition (effectively beta) or Nightly (unstable, updated every night).
You can get them from https://mozilla.org/firefox/channel/desktop/.
Then xpinstall.signatures.required will work again.
(As for permissions--you can create a GUI in a tab or a popup, but I don't think you can do it in a separate window (unless you do a webpage-style popup window). You won't be able to write to arbitrary files anywhere on the system--which is a good thing! You can write to the Downloads folder, and read/write some sort of internal storage, but that may not expose the actual files involved. For more information see https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Working_with_files.)
What you should be looking for is having your extension signed by Mozilla as Unlisted.
See Mixing Listed and Unlisted Add-ons on addons.mozilla.org blog post for an overview.
That way, AMO does not host nor (normally) review your extension; it simply runs some basic automated checks and immediately signs your extension so that it can be privately distributed as an XPI.
You can try setting the preference extensions.legacy.enabled (this will only work in Nightly or Dev Edition).
来源：https://stackoverflow.com/questions/47363481/install-a-personal-firefox-web-extension-permanently