Set FF_NETWORK_PER_BUILD to true in default-merge-request-variables

.gitlab-ci.yml

@@ -43,6 +43,7 @@ default:
 .default-merge-request-variables: &default-merge-request-variables
   NO_SOURCEMAPS: "true"
   ADD_SLOW_TEST_NOTE_TO_MERGE_REQUEST: "true"
+  FF_NETWORK_PER_BUILD: "true"
 
 .if-merge-request-security-canonical-sync: &if-merge-request-security-canonical-sync
   if: '$CI_MERGE_REQUEST_SOURCE_PROJECT_PATH == "gitlab-org/security/gitlab" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME == $CI_DEFAULT_BRANCH && $CI_MERGE_REQUEST_TARGET_BRANCH_NAME == $CI_DEFAULT_BRANCH'