The iOS Simulator is obviously a must have tool for development. Web development is no exception but Apple makes you jump through a few hoops (Xcode) to get to it. Luckily you can run it as a standalone application.
Copy this command on your terminal to create a symbolic link to it:
ln -s /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/Applications/iPhone\ Simulator.app /Applications/iPhone\ Simulator.app
It starts off ridiculously big but you can shrink it down by going to Window -> Scale -> 50%.