chore: add sync dev firefox action

.github/workflows/sync-dev-firefox.yml

@@ -0,0 +1,24 @@
+name: Sync Back to Dev Firefox
+on:
+  push:
+    branches:
+      - dev
+
+jobs:
+  sync-branches:
+    runs-on: ubuntu-latest
+    name: Syncing branches
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up Node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12
+      - name: Opening pull request
+        id: pull
+        uses: tretuna/sync-branches@1.4.0
+        with:
+          GITHUB_TOKEN: ${{secrets.SYNC_TOKEN}}
+          FROM_BRANCH: dev
+          TO_BRANCH: dev-firefox