Can't repro on Sierre w/ Firefox 61 & uBlock Origin installed. Which OS and browser version do you have? Any other addons that might be messing with stuff?

Do you still run into the issue in a private window w/o cache? Wonder if it's a caching issue.

I think the problem is that I'm not redirecting to 404.html properly, I'll look into it...

Edit: I got the same error using qutebrowser (WebEngine based) with no modifications. Checking if system settings might be messing it up?

Yup, can repro on that. Here's what I was able to do (cc @lachlanjc).

1. Open new Firefox 61 on Sierra through BrowserStack
2. Install uBlock Origin addon (Raymond Hill version)
3. Go to https://hackclub.com/notarealpage

This happens on Chrome too with ublock origin.

This happens for me on everything I try to access it on, including Chrome and Firefox with and without uBlock Origin, and on my iPhone. I don't think it's directly related to uBlock Origin or Firefox. The only difference I see is that on Chrome the error says "3" is undefined, but on Firefox it says "t.space" is undefined.

Its this line in the Nav.js component that's throwing the error for all of us: padding-left: ${({ theme }) => theme.space[3]}px; (line 36)

The page works fine for me (think this may have been fixed in one of @lachlanjc's recent updates). Closing, but comment here if you see it again