Unfortunately, according to the official Drosera wiki page, it's not available for the Windows version of WebKit/Safari (yet):
Drosera on Windows
Drosera is currently not available on Windows. Much of Drosera is written in JavaScript and should require very little modifications to run on Windows. The Cocoa application wrapper is not portable will need to be rewritten using native Windows APIs. Hop onto our irc channel if you're interested in porting Drosera to Windows.
So hopefully some enterprising individuals will take the initiative and do the port.
