I'm using Mozilla Firefox 81.0 and Kubuntu 20.04. When I load the front page or attempt to search for something, no titles appear in the gallery. The small swirling icon and "loading" text stay forever. Suspecting the problem might be with my browser extensions, I restarted Firefox in safe mode with tracking protection disabled and all add-ons disabled, but the problem persisted. I tested the site in Chromium and it works correctly.
Here is a video of the problem. Firefox is on the left, Chrome on the right.
Looking at the console, it seems that an API request results in an "Internal Server Error":