Back in the 90’s when I was working at Disney Online Alan Kay was a “Disney Fellow”. He split his time between Imagineering and DOL. He and a team of developers (that unfortunately didn’t include me) wrote a browser plugin for SmallTalk, ala Flash (well, Future Splash at the time). The team built a cool little game called “Yellow Submarine” as a reference implementation.
This all happened at the same time as MacroMedia bought Future Splash, turning it into Flash and then used their market power to get the installer included into everything.
After that the plugin project fell into obscurity.