Firefox: Switch Tabs with Keyboard

I was reading some comments on Flickr when somebody mentioned using Control+Option+Command+8 to polarize the screen. This is part of Mac OS X's "Universal Access" options found in system preferences.

So started playing around with this Control + Option + Command + ___ a little more. I found that if I hold the three buttons and press a number, it will select that corresponding tab on Firefox. For example, if I hold Control + Option + Command + 2, it will select the 2nd tab in the row.