Do you have a download limit for your dsl service? Perhaps you've passed over your monthly limit & are thus being shaped.
Have you checked for firmware upgrades for your billion model? It may be failing/dropping packets. Or else, your line from the isp is suspicious.
Overall it sounds like ISP bandwidth shaping.
As for your browser downlds failing, try another browser & see if you have same problems. I have 4 browsers on my computer. lol Sometimes one works better than others for particular sites & types of downlds. The issue might also be MIME file type settings in your browser; thus not being able to handle a particular filetype properly when attempting to downld it.