The only X Windows access from web browsers that I'm aware of is through something that was once called Broadway/XWeb, but I've never really seen anything use this.

I thought Broadway seemed like such a neat idea, back in 1997-1998, but it seems to have turned into something of a dead-end. I doubt that there are working plug-ins for recent browsers.

I bet you are actually trying to access to some X applications through a web interface. There are toolkits for interfacing to X-applications directly for testing purposes, that might allow you to interface a web app to an X app, but I doubt that such a thing would be a good idea.

If these X-apps have APIs and/or some standard database you could access, there might be some direction there toward a perl/web-app.