Theme does not work on Firefox, help!

Hey guys, I’ve been using a theme for a number of years and unfortunately it doesn’t seem to work as intended on Firefox, however it works on every other browser. Basically when you click on the subject link the blog post drops down and reveals itself, however on Firefox it doesn’t do that and instead there’s just a really long scroll bar on the side. Is there any way to fix this? Thanks!

My blog with the theme currently installed for reference:

https://matt.brownrug.org