So either it is using one of those fonts (Courier and Nimbus Mono L are similar I guess), the site is serving you special CSS that I'm not getting (and I've tested it on Linux and Windows), or Firefox has done some weird font aliasing and one of the above is being treated as Nimbus Mono L.
> "Inconsolata", "Source Code Pro", "Consolas", "Monaco", "Courier", monospace
So either it is using one of those fonts (Courier and Nimbus Mono L are similar I guess), the site is serving you special CSS that I'm not getting (and I've tested it on Linux and Windows), or Firefox has done some weird font aliasing and one of the above is being treated as Nimbus Mono L.