There are a number of add-ons for Firefox that clone Opera’s Speed Dial feature.  There is one add-on with a different twist.  Most open your tabs in this fashion, but Fast Dial does something different.

This extension will replace your “about:blank” page with a panel of thumbnails of your favorite web sites.  To add sites to the page, all you do is click on an empty cell, assign a URL and click OK.
You can also add sites by right-clicking on the [...]