Please make sure this pull request is tested properly before merging.

Does the wrapper work with firefox-bin?

Please rebase on the master rather than merging it.

If add-ons are removed and reinstalled, the settings are cleared. Is this an expected behavior?

1. Change directory to nixpkgs.

2. nix-build -I nixpkgs=. -o myfirefox myfirefox.nix
   where myfirefox.nix is the following file.

   let
     pkgs = import <nixpkgs> {};
   in
   pkgs.wrapFirefox pkgs.firefox-unwrapped {
     nixExtensions = [
       (pkgs.fetchFirefoxAddon {
         name = "ublock";
         url = "https://addons.mozilla.org/firefox/downloads/file/3679754/ublock_origin-1.31.0-an+fx.xpi";
         sha256 = "1h768ljlh3pi23l27qp961v1hd0nbj2vasgy11bmcrlqp40zgvnr";
       })
     ];
   }

3. ./myfirefox/bin/firefox -P test
   where test is the test profile.

4. Open uBlock settings and check Color-blind friendly.

5. Close the browser.

6. Reopen the browser to see the settings are saved.

7. Close the browser.

8. Rebuild the browser with empty nixExtensions (not null).

9. Open the browser, ensure the uBlock is uninstalled, and then close the browser.

10. Rebuild the browser with the uBlock in nixExtensions.

11. Open the browser and uBlock settings.

Expected: Color-blind friendly is checked.
Actual: Color-blind friendly is not checked.

Doesn't work with firefox-bin. Please make a separate PR for that.

let
  pkgs = import <nixpkgs> {};
in
pkgs.wrapFirefox pkgs.firefox-bin-unwrapped {
  browserName = "firefox";
  pname = "firefox-bin";
  desktopName = "Firefox";
  nixExtensions = [
    (pkgs.fetchFirefoxAddon {
      name = "ublock";
      url = "https://addons.mozilla.org/firefox/downloads/file/3679754/ublock_origin-1.31.0-an+fx.xpi";
      sha256 = "1h768ljlh3pi23l27qp961v1hd0nbj2vasgy11bmcrlqp40zgvnr";
    })
  ];

  extraPolicies = {
    CaptivePortal = false;
    DisableFirefoxStudies = true;
    DisablePocket = true;
    DisableTelemetry = true;
    DisableFirefoxAccounts = true;
    FirefoxHome = {
      Pocket = false;
      Snippets = false;
    };
    UserMessaging = {
      ExtensionRecommendations = false;
      SkipOnboarding = true;
    };
  };

  extraPrefs = ''
      // Show more ssl cert infos
      lockPref("security.identityblock.show_extended_validation", true);

      // Enable userchrome css
      lockPref("toolkit.legacyUserProfileCustomizations.stylesheets", true);

      // Enable dark dev tools
      lockPref("devtools.theme","dark");
    '';
}

If add-ons are removed and reinstalled, the settings are cleared. Is this an expected behavior?

Thanks for testing it! I can't change that behavior because this is up to the Firefox developers to decide how to handle the case when an extension gets removed through not being on the whitelist anymore. Upgrading addons works fine though

Doesn't work with firefox-bin. Please make a separate PR for that.

firefox-bin is incompatible with the wrapper. The binary does not load configuration from the /nix/store/*-firefox-*/lib folder. If you want to check it out yourself comment out these lines in the wrapper and then it builds:

        # For manpages, in case the program supplies them
        mkdir -p $out/nix-support
        echo ${browser} > $out/nix-support/propagated-user-env-packages

while at it can you also replace builtins.toFile by writeTextFile here ?
(currently this pr fixes one occurrence but not the other).

If add-ons are removed and reinstalled, the settings are cleared. Is this an expected behavior?

Thanks for testing it! I can't change that behavior because this is up to the Firefox developers to decide how to handle the case when an extension gets removed through not being on the whitelist anymore. Upgrading addons works fine though

Would be nice to document it though, so ppl can make backups of their settings.

while at it can you also replace builtins.toFile by writeTextFile here ?
(currently this pr fixes one occurrence but not the other).

Done

If add-ons are removed and reinstalled, the settings are cleared. Is this an expected behavior?

Thanks for testing it! I can't change that behavior because this is up to the Firefox developers to decide how to handle the case when an extension gets removed through not being on the whitelist anymore. Upgrading addons works fine though

Would be nice to document it though, so ppl can make backups of their settings.

Done

otherwise looks good; thanks for working on this by the way!
Even if it caused some confusion / fallout I very much appreciate that you manged to get this over the finish line :)