Merge branch 'release-v51.7.0' into release

Merge branch 'release-v51.6.0' into release

Merge branch 'release-v51.5.0' into release

Merge branch 'release-v51.4.0' into release

Bumped version to 51.3.0 (mozilla#2209)

Merge branch 'release-v51.2.0' into release

Merge branch 'release-v51.1.0' into release

Merge in release branch

Bumped version to 50.1.4

Merge branch 'release-v51.0.1' into release

Bumped version to 50.1.3