In general, enabling or disabling features depending on the browser is a very bad idea. You want to enable features depending on if the browser supports it, not if they are using a specific browser. For example suppose in 2012 you detected if the user was on Chrome, and only enabled Web Audio effects for that browser. Later Firefox adds support for Web Audio, and soon IE will as well, and you've unnecessarily crippled those browsers because you detected Chrome instead of Web Audio support.
You can detect the browser based on the user agent string, but all browsers pretend to be all other browsers because developers keep making that exact mistake over and over again. For example IE now pretends to be Chrome so developers who wrote browser tests instead of feature tests get fooled and enable the features which IE also supports. This makes it pretty hard to actually tell which browser it is from the user agent string. It's possible, but then if you do so, you're making exactly the same mistake all over again!
So don't do it. Think about the problem you are trying to solve and how to make it based on available features rather than the type of browser.