I don't get this. The issue had nothing to do with the language used.
It did have something to do with there being two languages used though, resulting in two different ways of excercising the network stack whith less testing for each. So its not a bug caused by Rust, but it is caused by the addition of Rust in Firefox.
This isn't specifically caused by rust, it's a second-system problem where they had two different ways to touch the http system and one was broken. It could have easily been the other way around with only rust being correct.
Yes, I know that, I'm trying to make the joke stand out but it's hard to do