The right scrollbar (as of Firefox 2.0) is set up so that, when the window is maximized, you can move the pointer all the way to the far right edge and still move the scrollbar, in accordance with Fitt's Law (makes it easier to hit the scrollbar, since it is infinitely large in the right direction).
RedShift V2 in the most recent pre-release version (as of this writing) added left and right borders to the window, saying it was to make it go better with dark OS themes (though, personally, I can't see the point in them at all no matter what kind of OS theme I set). The thing is, this breaks that Fitt's Law compatibility , so one cannot use the scrollbar at the far edge, but must make sure to hit it exactly (personally, this annoys me to no end).
This is just a simple style to fix that by removing the added borders.
.ad {
/* Your ad can be here instead. 10K unique visitors for $5/day. Mail me. */
}