BEage.
Responding to your questions in reverse:-
And anyway, what is allegedly wrong with IE6?
The general problem with IE (and MS software genrally) is its appalling security track record...
...and bloat. Their software is often very greedy for system resources and profligate in their use...
WTF is a 'tabbed browser'?
IE opens a whole window for every page. You want to look at two pages, perhaps to refer between them, or, as has been suggested here, to load up a number of slow pages simultaneously, and you get a whole new Window for each. This is a waste of system resources. A "tabbed" browser, like Opera or Mozilla opens one window and allows you to open multiple pages, each one selectable with a "tab" (a bit like workbooks in Excel). This is less resource intensive on your PC and make swapping between pages easier.)
HTH,
/RTFM