From https://support.mozilla.org/en-US/questions/928753#answer-338852 We did remove compatibility with tablets for Beta last Friday until we have the formal tablet UI ready. You can install Nightly on your tablet, but you will need to enable installation of non-market apps in your Android settings in order to do so (it is essentially the same as beta), again I apologize for the confusion and will get this documented today. http://nightly.mozilla.org ..we are figuring this out for tablets and don't have a perfect solution until we get to version 15 (when we plan to have tablet UI in beta).