Remove white space below image

In Firefox only my video thumbnails are displaying mysterious 2-3 pixels of white space between the bottom of my image and its border (see below).

I've tried everything I can think of in Firebug with no luck.

Any ideas how can I remove this white space?

You're seeing the space for descenders (the bits that hang off the bottom of 'y' and 'p') because img is an inline element by default. This removes the gap:

.youtube-thumb img { display: block; }