Browsing SO, I often find that my Firefox 15.0.1 on Gentoo Linux will fail to render monospace text exactly as monospace. As I haven't seen letters move when syntax highlighting kicks in, I assume that this is not due to Prettify, but instead an effect of the font rendering machinery itself. Using the Font Finder Add-On, I found that the font used is “Liberation Mono” from the 2.00.0 version of liberation fonts.
I'm not sure whether SO is in any position to fix this, so I won't mark this a bug. but I'd welcome pointers about how I could fix this for myself. Are any of the fonts with higher priority available for free? Has anyone experienced or heard about similar issues? What can I do to narrow down the list of possible culprits? For which package(s) should I report bugs?
The following screenshot comes from this post.