It is convenient to develop a WinForms application with a WebBrowser component because Word documents and other files can be opened in it. The only problem I found last week was that BMP files cannot be opened inside.
I guess the reason for that difference is that BMP is not a compressed format, which is not suitable for Internet usage. If it is the reason, then why Firefox supports BMP very well?
After all, when you want to Navigate() to a BMP file, stop. You should convert the image to GIF/JPEG/PNG format instead.