I know this may not be the best place to ask this question, but I'm comfortable here and I trust you cats to give me a straight answer before a bunch of (even more) highly-strung zealots on a browser message board. Can anyone explain why some websites just won't work with Firefox on some wireless connections?

Here's my problem: there is a coffee shop in my neighborhood with great coffee, good food, and free wi-fi, so I spend a lot of time there. But I can't for the life of me get some sites to open through Firefox (on a Mac) via their connection, major sites like the New York Times, Chicago Tribune, and my bank, not just my crackpot uncle's blog served out of a Commodore 64 in his basement. I sometimes have luck with Safari, but even with that I can't connect to my bank's site. When I'm at home and just about any place else, they all work fine. I can understand if their net connection was just generally crappy, but most sites, RSS, and other things work fine. Why would it crap out on just a few?