For scripting on web browsers, the only option now is using javascript.
I wonder if Ruby ever could make it to the web browsers?
It's highly unlikely cause MS doesn't have any reasons for letting Ruby to become first class citizen, wouldn't that be bad for their current platform? I don't know how Apple sees it.
If Ruby can't be first class citizen in the browsers, how likely is it that a add-on could be installed on the browser, letting the browser execute Ruby also. In that way, we programmers could just use Ruby instead.