Hello,
I've updated the theme selector block for Moodle 2.9 - 3.4: https://moodle.org/plugins/pluginversion.php?id=15183. It comes with a new feature that allows you to create a browser window of a given size which is really useful in creating consistently sized screen shots of your theme for presentations etc.
If you find this post useful, then please mark it so.
Cheers,
Gareth