I don't get why Google didn't do this already. It's pretty intuitive and desktop applications such as iCal do a similar icon preview.
The reason why I gave this script 4 stars is because it doesn't work on HTTP at the time of this writing. If the author of this script is reading this, you can just fix it by adding another @include line with the same thing but an HTTP prefix instead of an HTTPS
This script caused me to have to shut down my computer twice, even after I disabled the script. With this script running, if you click on a mailto: to open an email window it causes multiple tabs to open and the only way to shut it off is to disable the script and force close the firefox browser. then when you re-open, you have to close 100 tabs. Super annoying and I hope it didnt do any permanent damage.
* Title is too short (minimum is 4 characters)
* Body is too short (minimum is 5 characters)