This article by Christian Heilmann (of Mozilla and Microsoft fame) about the misconception that expecting certain features and capabilities in browsers and simply stating "please upgrade/turn on/go away" if these "requirements" are not met by the user's set up is web development is very much worth your time if you create things for the web.
And no, your shiny new client-side JavaScript framework is not the problem, but it isn't the answer, either.

Here’s a reality check — this is what our users should have to do to consume the things we build:

That’s right. Nothing. This is the web. Everybody is

...