I'd say about 90% of the code can be cross platform; some things you'll have to implement seperately, such as the drawing library, since that doesn't work the s

I'd say about 90% of the code can be cross platform; some things you'll have to implement seperately, such as the drawing library, since that doesn't work the same on each platform. FireBreath abstracts most of the differences, though. For example, it isn't a shim to let npapi plugins work on activex; it's a shim for both npapi and activex plugins, which means it's easier to write something in firebreath than it is to write it using npapi as well. If you aren't doing any drawing, just network stuff and calculations, you can probably get by without writing any platform specific code. - Taxilian (original author of FireBreath)