This has been bothering me a lot since I got my Hero a few weeks back: When connected to a Wi-fi network, the browser would just hang when trying to load any page. Both the built-in browser and Dolphin. Opera 5 worked, but cannot (yet?) be set as the default browser. All browsers worked fine when using the 3G connection.

However, it turns out that this is really easy to fix: Disable the proxy setting in the “mobile network”. Full description (from this comment):

The only way I could get it to work was to remove the proxy setting as follows:
Go to Menu -> Settings -> Wireless Controls -> Mobile Network Settings -> Access Point Names and select the APN. Remove the entry from the Proxy field (should say <Not set> for wifi browsing to work). Press Menu -> Save and now you should be able to browse the Internet over wifi and 3G browsing should still work.

Works perfectly for me and I have not seen any adverse effects so far. Thanks, ZimGuy 😉