The problem seems to be simply that MFCEmbed does not implement ShowAsModal().
When WindowWatcher makes a new modal window, it tries to call this. MFCEmbed
just returns NS_ERROR_NOT_IMPLEMENTED.
My fix was simply to borrow some code I found in WinEmbed (its version of
ShowAsModal()) and modify it slightly to make it work. I've attached a patch
for BrowserImpl.cpp. (Or at least I've tried to... I am not yet learned in
the ways of diff and patch... Sorry if it's not a proper patch.)
Well both really. The code has been put into the latest beta, which means it will also be in the final release of 0.7, as it fixes one of the problems that K-Meleon has been experiencing.