Do you mean a web browser? If you're looking for the ROM of the official one, we can't give you that, as the rules strictly forbid warez. And you'll need a slot-2 flashkit to be able to use it, anyway.

Otherwise, there are some homebrew web browsers that work straight from slot-1 (your R4) without the need for any slot-2 flashkit. You should be able to find them all in the Download Centre. I prefer using Bunjalloo, as it's the easiest and the fastest one.