thesourceeternal
commented
10 years ago http://stackoverflow.com/questions/11871077/proper-way-to-detect-webgl-support (user2070775 explains something specifically for three.js and points to this: https://github.com/mrdoob/three.js/blob/master/examples/js/Detector.js)
doc from free node channel #webgl gave these links: http://codeflow.org/entries/2013/feb/22/how-to-write-portable-webgl/#how-to-get-webgl (he says, "you'll also want to consult all the other chapters, there's a lot more to it than simply checking for webgl availability") He's also doing this: http://webglstats.com
If a person doesn't have the capabilities to run the game editor or game, they should have a message on their screen explaining that. Ideally a message about what capabilities they're missing, but I don't know if that's possible.