[Bug]: Show "Request was throttled ..." instead of "An unexpected error occured" for the abuse reports addon endpoint

[ioanarusiczki]

What happened?

From https://github.com/mozilla/addons/issues/14931#issuecomment-2262712333

After hitting the throttle for the abuse report addon endpoint the frontend displays the following error:

What did you expect to happen?

It is not reproducible for the other abuse report endpoints: collections, ratings, users.

Is there an existing issue for this?

• [X] I have searched the existing issues

┆Issue is synchronized with this Jira Task

[diox]

This happens because the error isn't handled in exactly the same way when the request goes through Firefox's built-in navigator.mozAddonManager.sendAbuseReport() API.

To reproduce locally:

• Use Firefox (other browsers don't have that internal API)
• Configure Firefox extensions.addonAbuseReport.url to hit the env you want to hit (by default that pref points to prod. Make sure to reset if once you're done!)
• Configure Firefox + your env to be allowed to use mozAddonManager.
• Submit anonymous abuse reports (to avoid accidentally bypassing throttles if your user has the permission to do so) against an add-on until you hit the threshold (currently 20/day).

If all these steps are followed, you'll see the An unexpected error occurred. If any of the initial steps are skipped, you won't reproduce the problem and will see Request was throttled.