Merge m-c to fx-team, a=merge

MozReview-Commit-ID: 3UVypl5oC1y

testing/taskcluster/tasks/tests/fx_linux64_mochitest_gl.yml

@@ -18,4 +18,3 @@ task:
       groupName: Desktop mochitests
       groupSymbol: tc-M
       symbol: gl
-      tier: 2

testing/taskcluster/tasks/tests/fx_test_base.yml

@@ -31,7 +31,7 @@ task:
   extra:
     treeherder:
       groupName: Desktop tests
-      tier: 2
+      tier: 1
     treeherderEnv:
       - production
       - staging