lame I had a similar problem with AOL...Really pi$$ed me off when I was playing games online and the thing would switch to windows and that stupid idle timer makes its noise...
It would also do it while I was using an internet browswe, as in your case...Changing ISPs was the only solution I could come up with.
Now I am with OzeMail with a 12 mth contract, 25 dollars a month, first three months free, no time limits, no idle disconnects, good speeds.....Im happy !!