Just in the last day, the site's look has become completely broken for me, it now looks like this: imgur.com/a/k1d8MAU

I tried disabling all my extensions on Firefox but that didn't fix it either. Is this happening for anyone else?

I assume this means it's just a me problem then? Does anyone have any advice on how to fix this?

Have you tried using another browser? Is there anything that shows up abnormally if you check the console? (F12)

Never happened to me, but I would reinstall Firefox and try again while keeping the browser settings default. Could also be that the files responsible for the theme get blocked by something, but that would be very hard to troubleshoot over forum messages.

Well, somehow the problem fixed itself? I have no idea what I did or didn't do to fix it but the site theme works now. Very weird.

No problem with "theme", just with the captcha that not only require toggling off NoScript, but now also Adblock Plus, otherwise it doesn't load, or disappear before you can do anything.
Maybe it's related?

Try a different adblocker. I've had zero issues with uBlock origin. It's functionally identical to ABP.