everything in the 'defaults\profiles' directory is there for the purpose of generating new profiles... if you get rid of it, and something happens to one of your profiles that requires restoring a file from the defaults, k-meleon won't be able to do it... it's both a backup and an original source. think of it as DNA or something
as for the error playing the throbber, that would have to do with whatever program has .avi files associated with it, not with kmeleon.