User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:20.0) Gecko/20100101 Firefox/20.0 Build ID: 20130409194949 Steps to reproduce: Visited several web forums with different version of Firefox for Mobile (16-21). Actual results: The Reader Mode icon is no longer offered for these sites in Firefox 20 or 21. Expected results: Reader mode should not be disabled in "low-memory devices" (see bug 852417) for those who want this feature. I vote to re-enable this feature, or at least offer a hidden preference, since the increased functionality offered by Reader Mode far outweighs any performance improvements gained from turning that feature off.

Nightly now has a preference in about:config to force an override; feel free to try it out: reader.force_allow set that to true.