How can Fluid be using an old version of Safari? Does it bundle its own build of WebKit? Or are all Mac apps that use the public WebKit framework using an older version of WebKit than Safari itself?
I'm also using Fluid, and I even purchased a license for it, but it seems like it's no longer being maintained, to the point where sites refuse to work with it due to the outdated User Agent Identifier (which you can change, but still...).
Fluid refuses to create a wrapper for a site using a self-signed SSL certificate (or at least, it did the last time I tried it).
This was annoying, because I wanted to use it with an app I was self-hosting, and it wasn't worth the effort of getting an SSL certifiate it would accept.