I have wanted this feature for years. Back when I used OSX, there was a plugin I could use that allowed me to set a webpage for my screensaver. Today I finally found an implementation doing the same thing in Linux.
It was implemented by a guy named almost 2 years ago according to the git activity.
You can view his repo for installation instructions. Simply clone/download the webscreensaver file in the repo, make it executable, place it in /usr/lib/xscreensaver/ and edit your ~/.xscreensaver file.
It works perfectly for me. I use it display several of my experiments from my lab
