Revert "chore: disable Firefox WebTransport interop tests (#2930)"

This reverts commit 15a70af.

Author: achingbrain

interop/firefox-version.json

@@ -2,6 +2,10 @@
   "id": "firefox-js-libp2p-head",
   "containerImageID": "firefox-js-libp2p-head",
   "transports": [
+    {
+      "name": "webtransport",
+      "onlyDial": true
+    },
     {
       "name": "webrtc-direct",
       "onlyDial": true