Where did you receive the snippet from? The possibilities are just about infinite as to what that could be - piece of AI maybe that fell from the sky, maybe a chip off one of those jpgs google dropped on the floor. Out of context, who knows?

When these files first started appearing, instead of saying the website it was from, the downloads list said it was a moz-safe-about-resource. This would be on the file's entry on the Downloads list (Command+J).

Example thread: https://support.mozilla.org/questions/1443648

Because these files are empty, it's not possible to determine what the site was actually trying to get Firefox to load based on what happened in the past. If you find a page that consistently triggers the problem, a volunteer could take a look at it.

jscher2000 - Thank you for your helpful response. The notification popped up on my home screen. It had a Firefox logo and did say "moz-safe-about- resource". When I hit Command+J, it shows "no downloads." However,when I access downloads via Finder, it shows as "xRqj7qhl.html - Size: zero bytes - Kind: HTML text". I'm not tech savvy, so my question is "might this be dangerous i.e. a virus attack?" If you have an opinion on that, I'd appreciate it.

A zero byte file is empty and can't do anything. You can just delete it.