Subscribing to Novičnik not working on Firefox

[svigelj]

Problem

When I try to subscribe to Novičnik on Firefox it fails with the following error:
The resource at “<URL>” was blocked because content blocking is enabled.

Reason

This might be the reason.

Workaround

I was able to successfully subscribe via Chrome.

[greenstatic]

Confirmed.
It’s also possible to disable content blocking per site (Firefox) to be able the subscribe to the newsletter, however this is not a proper fix.

Some error handling is required to warn the user instead of errors in the console.