The browser is still WIP, a lot of pieces are still missing(Content Picker, Download manager, Private browsing) they will be integrated in the next months, also the browser will switch to Oxide(based on Chromium Content API).
The prefetch is an option which you can opt-out from, and i think you are mixing prefetch and prerender, just to let you know Firefox has actually supported prefetching since...wait for it... 2003.
Yes, look at my example (http://jsbin.com/utugex/1/edit), the href is pointing to an .html file, so in the normal case the browser will display the content of the page but with the download attribute the browser will be forced to download it as "myfile.pdf".