It's unfortunate that it's not available for Firefox mobile, for me at least, mobile is where I want translation. For example when traveling and viewing the sites of businesses
However on the plus side, I'm not seeing a complete inability to translate in Nightly since the context menu let's me translate using Google Translate (i realise many won't want to send their text off to G but this does at least show up one of the claimed limitations in the article, that it simply wasn't possible at all)
What is the technical requirement behind this?