Remove white space below image [duplicate]

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.

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; }

You can use code below if you don't want to modify block mode:

img{vertical-align:text-bottom}

Or you can use following as Stuart suggests:

img{vertical-align:bottom}

If you would like to preserve the image as inline you can put vertical-align: top or vertical-align: bottom on it. By default it is aligned on the baseline hence the few pixels beneath it.