buildMozillaMach: add support for MLS

We have received our very own API key for Mozilla Location Services and
have been recognized as a Public Interest Project, implying a rate limit
of 100k daily requests¹, which should be sufficient for our population.

N.B: This key belongs to the NixOS project, please don't use ours, but
instead request your own.

[1] https://location.services.mozilla.com/terms

pkgs/applications/networking/browsers/firefox/common.nix

@@ -102,6 +102,7 @@
 , crashreporterSupport ? !privacySupport
 , geolocationSupport ? !privacySupport
 , googleAPISupport ? geolocationSupport
+, mlsAPISupport ? geolocationSupport
 , webrtcSupport ? !privacySupport
 
 # digital rights managemewnt
@@ -298,6 +299,12 @@ buildStdenv.mkDerivation ({
     # 60.5+ & 66+ did split the google API key arguments: https://bugzilla.mozilla.org/show_bug.cgi?id=1531176
     configureFlagsArray+=("--with-google-location-service-api-keyfile=$TMPDIR/ga")
     configureFlagsArray+=("--with-google-safebrowsing-api-keyfile=$TMPDIR/ga")
+  '' + lib.optionalString mlsAPISupport ''
+    # Mozilla Location services API key
+    # Note: These are for NixOS/nixpkgs use ONLY. For your own distribution,
+    # please get your own set of keys at https://location.services.mozilla.com/api.
+    echo "dfd7836c-d458-4917-98bb-421c82d3c8a0" > $TMPDIR/mls-api-key
+    configureFlagsArray+=("--with-mozilla-api-keyfile=$TMPDIR/mls-api-key")
   '' + lib.optionalString enableOfficialBranding ''
     export MOZILLA_OFFICIAL=1
   '';