For Firefox 4 for Windows, there is a really useful image-block addon for slow connections: https://addons.mozilla.org/firefox/addon/quickimage/
Unfortunately, Firefox mobile is pretty slow and the addon doesn't exist for it. Most browsers can turn off image loading in options/settings. But often this causes a horrible site look. Blocking only 3rd-party image sources really makes browsing on 64kB/s mobile connections a lot faster. Generally, you don't need things like Opera Turbo Mode, it's not like DSL speed, but sites load within 5-10 sec.
So is there a way to block 3rd-party images by default? Tools like AdBlock don't show images with distinct paths (, but download all images by default?). I'm not looking for something like Opera Mini or Opera Mobile Turbo mode. I know these options.
I found a solution for Firefox (built-in config setting). I keep the question open, as someone may find to do the same thing on Dolphin HD or Opera. Then Dolphin would become my standard mobile browser.