feat(test): add MOZ_AUTOMATION=1 to ff test runner (#2049)

this ensures that ff launcher on windows wait for browser instead of creating detached instance and quitting
for more info see ff wiki:
https://wiki.mozilla.org/Platform/Integration/InjectEject/Launcher_Process/#Starting_Firefox_via_Automation_.2F_Scripting

pkgs/test/CHANGELOG.md

@@ -8,6 +8,8 @@
 * Add support for `SAFARI_EXECUTABLE`, `FIREFOX_EXECUTABLE` and
  `MS_EDGE_EXECUTABLE` for custom browser installations.
 * Allow the latest analyzer (6.x.x).
+* Add `MOZ_AUTOMATION=1` environmental variable to Firefox runner, to make
+ launcher process on Windows wait for browser exit.
 
 ## 1.24.3
 

pkgs/test/lib/src/runner/browser/firefox.dart

@@ -47,7 +47,8 @@ class Firefox extends Browser {
  '--no-remote',
  ...settings.arguments,
  ], environment: {
- 'MOZ_CRASHREPORTER_DISABLE': '1'
+ 'MOZ_CRASHREPORTER_DISABLE': '1',
+ 'MOZ_AUTOMATION': '1',
  });
 
  unawaited(process.exitCode.then((_) => Directory(dir).deleteWithRetry()));