In Chrome, you can pretend to be a device that supports touch and emulate touch events directly within the browser. To do this open the Settings panel (the cog icon in the bottom right of Chrome Developer Tools), select the "Overrides" option and choose "Emulate Touch Events".

In Chrome Canary, this will replace the cursor with a circle so you can not only tell which mode you are in, but also how large the surface area for a touch click may be.

Firefox's Responsive Design View gives you the option to emulate touch events