Took off circular rubber thing, now low-beam won't turn on [pics]

[Red0x]

I was playing around under the hood and idiotically pulled off a piece of rubber near the passenger headlight that didn't seem like it should do anything, but now the low-beam for that side won't turn on.

Pics. The first pic is the passenger side with the rubber removed and set upside-down next to the plastic thing it was sitting in. The 2nd pic is the driver's side version which is still intact.

I tried to put the rubber back in but it's very difficult because of its shape.

What is this thing? Is it related to my low-beam not working? How the heck do I fix this? Feel free to call me an idiot (doh).

 

[Fiji Mazda3]

Was it on the back of the headlight itself?

 

[Red0x]

Not on the back, more like on top and to the side. I'm thinking it was just really bad luck that it burned out at the same time I took this off. I'm pretty sure it's just a spacer for the hood. I'll try replacing the bulb.