Another problem with associating an application's icon directly with the task it performs is the large number of programs that all do the same thing. Once we design an icon that accurately represents what a web browser does, which web browser gets to use it? How about video players and text editors of which there are dozens. And what kind of icon would work better for an RSS reader? I suppose one possbility would be a newspaper, but even that metaphor breaks down when you think about it. How do we graphically represent concepts that have no direct visual analog?

I think the criticism is a valid one, but I fail to see how the problem can really be solved. It's not just a matter of "computer vocabulary". There's also branding and just simply disambiguating one web browser (or whatever) from another. The mozilla folks are going the right direction with their icon design. There is no accurate graphic representation for what a web browser does (not really) so they're instead choosing to develop a strong visual brand identity to separate themselves from the other browsers. I think it's a good design strategy that will ultimately serve them well, probably better than a more utilitarian solution would.