Loading Docs Into Frames

How come my browser, namely ie6, can reload(or load from favourites) a frameset and remember which documents were loaded into the frames without a query string?

I need to capture this in javascript so I can make sure my frames are inside the correct frameset yet still allowing users to load up with a particularly favourite doc. This is not done using a query string, or does not appear to be, so how is it done?

For example I load a frameset doc named index.html which contains 2 frames namely header.html and main1.html, main1.html has a link which loads main2.html into it's own frame. Now I add to favourites with main2.html showing. Next I go to a completely different site, delete all cache etc and close down IE. Then starting IE afresh I load the saved favourite and with no query string it loads main2.html.