This would be very useful for me but every time I open this in firefox, the tab just crashes (tried with no extensions as well) It does work on badwolf, and probably also on other webkit/chrome based browsers, but it's too much for firefox.

Looking at the html file, I think you need to break the file down in smaller chunks, because that is huuge. 70mb is quite a lot for an HTML file.

You or may not be surprised to learn that the reason these index files are so large is because I have compressed every loaded class into them.
The actual HTML content is tiny because I compute it on demand. What takes up so much space is the JSON containing all the class data.
A new version of the compressing algorithm is in the works right now, but I’ve been quite busy as of late, preventing me from working on it right now.

I have a couple of experimental versions I am working on, but so far the file sizes are significantly less.
For default Fabric, it is currently at ~24-27 MB for default Forge it is <10 MB total.

Forge (Experimental) 1.18.2: https://hunter19823.github.io/kubejsoffline/exp/1.18.2/forge

Fabric (Experimental) 1.18.2: https://hunter19823.github.io/kubejsoffline/exp/1.18.2/fabric

works like a charm so far! Very nice!