TypeError: nav.useragent is undefined

[Federico]

Hi

According to http://www.useragentstring.com/ i'm using "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:29.0) Gecko/20100101 Firefox/29.0" , which is correct: i'm using "distribution" firefox (i didnt recompiled or anything strange, just instaled with apt-get) on linux mint14
The demo page just keeps on "loading" and JsConsole says "

TypeError: nav.useragent is undefined
  if (nav.useragent.toLowerCase().match(distros[i].toLowerCase())){

I've installed Ghostery (https://www.ghostery.com) but just in case i've whitelisted the demo site.