Firefox fails to install - blocked?

Hello!

I’m seeing some recurrent issues where downloading Firefox ESR from the Mozilla services hangs. After 10 minutes, the build times out and is marked as “errored”.
I am using the following build configuration snippet to install Firefox:

addons:
  firefox: latest-esr

I am seeing it happen more often when multiple builds are running concurrently. Is it possible that Mozilla is blocking or rate limiting Travis IPs? Should Travis be caching the download instead?

When running this, are you also installing dbus?

addons:
  firefox: "latest-esr"
  apt:
    packages:
      - dbus-x11
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