BRE-883 build(firefox): check file size (#15399)

* build(firefox): check file size

if building `firefox` or `firefox-mv3`

    * check if any file(s) exceeds 4M (megabytes)

        - If true, fail and provide basic message.

* style: add clarity

sytle: add error message

* fix: relocate step

ensure final step of source files before validating

* test: add failure condition

* fix: source file target directory

* fix: test for failure condition

* test: remove failure condition

remove lines used for testing

.github/workflows/build-browser.yml

@@ -268,6 +268,29 @@ jobs:
         working-directory: browser-source/
         run: npm link ../sdk-internal
 
+      - name: Check source file size
+        if: ${{ startsWith(matrix.name, 'firefox') }}
+        run: |
+          # Declare variable as indexed array
+          declare -a FILES
+
+          # Search for source files that are greater than 4M
+          TARGET_DIR='./browser-source/apps/browser'
+          while IFS=' ' read -r RESULT; do
+              FILES+=("$RESULT")
+          done < <(find $TARGET_DIR -size +4M)
+
+          # Validate results and provide messaging
+          if [[ ${#FILES[@]} -ne 0 ]]; then
+              echo "File(s) exceeds size limit: 4MB"
+              for FILE in ${FILES[@]}; do
+                  echo "- $(du --si $FILE)"
+              done
+              echo "ERROR Firefox rejects extension uploads that contain files larger than 4MB"
+              # Invoke failure
+              exit 1
+          fi
+
       - name: Build extension
         run: npm run ${{ matrix.npm_command }}
         working-directory: browser-source/apps/browser