Thanks for the response!

So,

I click the link. I click "Add", and Mozilla says addon could not be downloaded due to connection failure. Nothing appears in browser console.

Downloading an addon gives me "Download failed. Please check your connection." on the Addons site. In console, I get:

  Events to handle the installation initialized. BigInteger.js:27
  [GA: OFF] sendEvent {"hitType":"event","eventCategory":"AMO Addon Installs Download Failed","eventAction":"addon","eventLabel":"uBlock Origin"} BigInteger.js:27
  Error:

In the studies, I have https://i.imgur.com/fqrd5Jo.png. I enabled it, and have tried setting both first run, and the update interval is set to 21 (to try and force it to update it quickly).