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Historically, the browse button has been quite resistant to changes in appearance, since it's basically hardwired into the client's OS. However, this is the old story, and I haven't looked into it lately. Things have been changing.
There is a very thorough FAQ on forms and Javascript at [developer.irt.org...]
I looked through it, and didn't spot the exact info you need (although some of it comes close.) But this is a VERY big bunch of information, and you may want to double check me.