I'm running FireFox 20 and I noticed that the feedlink icon was no longer showing up in my toolbox. I saw that it's hidden in FF2Fixes.css. In /skins/common/wikibits.js:
window.ff2_bugs = /firefox\/2/.test( clientPC );
It looks to me like FireFox 20 is being read as FireFox 2, and thus the feedlink icon is being hidden. I'm sure this will be an issue for all of FireFox 20-something version numbers.