How can I keep my xp theme from interfering with web page colors in Firefox?

I've started using a darker theme with white text and dark fields. It's working great except for certain text fields on the web. Example: Google Maps' search field is fine, but the Get Directions: A and B fields are black field on black. I don't have firefox set to use system colors for font/ field colors, but my guess is the web pages themselves are looking for the system colors and using them as if I had the default black on white scheme. The result is black text in a black input field. Not every field but some fields. Is there a way I could point the site to the standard / classic theme whenever it looks for the system colors?