Update build.yml

.github/workflows/build.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         node-version: [10.x, 12.x]
-        browser: [chrome]
+        browser: [chrome, firefox]
     steps:
     - uses: actions/checkout@v1
 
@@ -58,12 +58,15 @@ jobs:
     - uses: cypress-io/github-action@v1
       with:
         browser: ${{ matrix.browser }}
+        group: ${{ matrix.browser }}
         headless: true
         command-prefix: 'percy exec -- npx'
         start: yarn dev
         wait-on: 'http://localhost:9000'
         install: false
         working-directory: cypress
+        parallel: true
+        parallelism: 4
       env:
         PERCY_TOKEN: ${{ secrets.PERCY_TOKEN }}