Similar thing I made recently, but as a Chrome extension:

https://github.com/szhu/pagefreeze

It does the same thing, and in addition also prevents any async JS from running. It also can be easily toggled per-site; just click the extension icon! Unfortunately I didn't have time to put a GIF in the README. OP did a better job of explaining what their project does!

Would love feedback on it + hope it helps someone as well!