Just found this, when you’re in Dashboard, press → (right arrow) to go Next page and ← (left arrow) to go Previous page, been wanting this forever and didn’t know it existed til now. Thanks marco and team!

Here is what worked for me with Firefox 6:

Install the keyconfig addon from the keyconfig download page and restart.
Go to Addons -> keyconfig -> Preferences.
There are no "Previous Tab" and "Next Tab" entries by default, but you can add them by clicking Add a new key and using the following code snippets (thanks to the author):
Next Tab: gBrowser.mTabContainer.advanceSelectedTab(1,true);
Previous Tab: gBrowser.mTabContainer.advanceSelectedTab(-1,true);
Assign whatever keys to the "Next Tab" and "Previous Tab" actions.
(The Customizable Shortcuts addon didn't work for me, as it didn't have entries for Next Tab and Previous Tab.)