As far as I can figure out, its NOT part of the firmware...But this can be made into a general purpose browser if you create a portal-like site to jumps to links. When you select "Go to home page" it returns you to the portal site (index.html). So that's an easy way out.You can find the full article here
Yes you can use input (we googled stuff), when you enter a textbox and press X the PSP pops up the Keyboard API (remember there's alot of API to be taken advantage of with the PSP). After that its as simple as any other input on the PSP.
Howto find the Sony PSP's hidden web browser
Posted on Wednesday, March 30 2005 @ 2:14 CEST by Thomas De Maesschalck
Some smart people found out that a Sony PlayStation Portable (PSP) game called Wipeout Pure contains a full-featured web browser!