Thank you for creating a really useful add on for firefox, it is true that an image worth more than thousand words.
Can I suggest a feature?
every sometime all websites gets a make over or just a change of background. Can I suggest that the tumbnails update to show the last appereance of a website?
Also because some webpages have pop up adds that the tumbnails think are the main page (like those from AdWorldmedia that cover the main page)
Best Wishes and success.