I know this is most likely an issue on my Linux machine but I haven't seen it on any site besides the rust docs... Is anyone else seeing this?? Any ideas what might be going on?
I access the rust documentation from two different linux machines pretty regularly (Mint 17.1/17.2 xfce) from Chromium. I have seen this problem once or twice, and a refresh usually fixed it. I just assumed I was pulling the data at the same time new versions of the docs where being pushed up to the server.
dev is the name of a profile which must be new. If you already have one called that, change dev to some other name and create that new profile in the profile tool.
If that fixes it, go back to your normal profile and do Options -> Help -> Troubleshooting information -> Refresh firefox in the top right. Choose whatever settings you prefer in the dialogues.
Sure enough, looks like the sidebar is using the "Fira Sans" font, which appears to be busted on my system. If I use Chrome's dev tools to remove that font from the font-family list for the sidebar class everything shows up!