MB 15: Prepare Mullvad Browser release 12.0a3

projects/firefox/config

@@ -80,6 +80,7 @@ targets:
     var:
       branding_directory_prefix: 'mb'
       browser_branch: '12.0-1'
+      browser_build: 1
       gitlab_project: https://gitlab.torproject.org/tpo/applications/privacy-browser
 
   linux-x86_64:

rbm.conf

@@ -252,6 +252,8 @@ targets:
       exe_name: mullvadbrowser
       updater_enabled: 0
       locales: []
+      torbrowser_version: '12.0a3'
+      torbrowser_build: 'build1'
 
   torbrowser-testbuild:
     - testbuild