Opensource browsers, and browsers in general, have developed a lot in the past 10 years or so. And so has the web; it is simply much more complex & demanding than it used to be. So there's some compatibility problems which might lead to javascript breaking in weird ways. Add to that all the trouble you get because encryption doesn't work anymore on these outdated browsers... And yes, even a cheap Android phone nowadays has more oomph than an N9. (And the graphical UI of a mobile phone OS needs to keep much more stuff in RAM than, say, a normal Linux desktop)