Add firefox to browser tests

.github/workflows/ci.yml

@@ -143,6 +143,11 @@ jobs:
         path: ./src/github.com/maputnik/desktop/bin/windows/
   
   cypress-run:
+    strategy:
+      fail-fast: false
+      matrix:
+        browser: [chrome, firefox]
+
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout
@@ -154,4 +159,5 @@ jobs:
         uses: cypress-io/github-action@v6
         with:
           build: npm run build
-          start: npm run start
+          start: npm run start
+          browser: ${{ matrix.browser }}