eee pc+ubuntu 9.04+three mobile broadband - why do some sites not load in Firefox or Chrome?

eee pc+ubuntu 9.04+three mobile broadband - why do some sites not load in Firefox or Chrome?

When I'm using my three mobile broadband dongle, I've noticed that some sites (including stackoverflow.com and my wife's blog) won't load in Firefox or Chrome but will in Opera or with curl and wget.