Since the latest Construct 2 update, I've found gamePad button inputs to be very laggy. I'm running Firefox 32.0, and the controllers I'm using are Afterglow Xbox 360.
I made the above capx for a bare-bones test. Both layouts use the same event sheet with just two events: playing some music on the start of the layout, and playing a sound effect whenever the A button of controller 0 is pressed. Try mashing the A button as fast as you can on both layouts.
The first layout has nothing on it. On it, you can make a lot of noise if you press the A button as rapidly as you can.
For the second layout, I threw a handful of black tiles with the solid behaviour as well as a couple of sprites with the platform behaviour and all its default settings. If you rapidly press A on this layout, distinct gaps will appear between the sound effects.
My game - pretty much every game - is going to have a lot more complexity than this, and pressing a button a lot is probably desirable for many of those games. I seemed to not have this problem before the update. Has anyone else noticed this?
Edit - Huh! I can't share a URL? Well... it's an easy enough capx to recreate, I guess. The most minimal steps were taken, exactly as noted here.