From the pointy board...
Sounds like some a-hole left a firework on top of the car, which caught the top on fire. The car certainly looks like a total loss to me:
http://forum.miata.net/vb/attachment...achmentid=1397
http://forum.miata.net/vb/attachment...achmentid=1399
http://forum.miata.net/vb/attachment...achmentid=1401
Be careful out there today and watch for the idiots. :-?