LiveReload - Better Than Batman and Robin
|Batman and Robin by MrSchuReads (CC BY-NC-SA)|
LiveReload is an OS X app (~$10). It watches the directories you give to it and then refreshes your browser if its contents get modified. In order to do this you'll need a browser plugin. You will also need to connect your browser to the host app. After this you are good to go.
It is also possible to run some custom script of your own before refreshing the browser. I use this to compile my project using RequireJS builder.
Apparently some people tend to favor CodeKit instead of LiveReload. This fine article has more insight on that. I'm sure there are some other alternatives out there as well. It's definitely worth your time to research and find some solution like this. The investment is bound to repay itself in form of improved productivity. Getting more done with less effort is always good.