I updated Firefox Mobile Beta on my Samsung Galaxy SII a couple of days ago to version 16 and out of curiosity I participated in the pissing-contest which is html5test.com. It scored a whopping 372 points, which apparently makes it the best mobile browser (for now).
More important, as it is an immediate and noticeable advantage: reader mode. Reader mode, as seen in the screenshots on the right, allows me see articles on e.g. the chaotic, non-responsive dewereldmorgen.be in a non-crowded context which is optimal for reading the article.
I also installed the latest Firefox Mobile Aurora (version 17) and I’m pretty pleased to see support for iFrame sandboxing (which would up the html5test.com score to 377) and integration with a.o. the upcoming Firefox Marketplace (which will also be core to Firefox OS).
So yeah, for me Firefox Mobile remains the best mobile browser no-one uses.