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.)

Ah, tabs.

Tabs, tabs, tabs. The specialist subject of UI experts everywhere. Should tabs just rearrange horizontally or also detach? How much vertical scroll buffer should a tab have before it detaches? Under what circumstances should it detach? What about reattaching?

This is a short piece concerned only with the different behaviours when closing tabs in Google Chrome, as I think these behaviours are fantastically thought through.

Ett tillägg till Firefox för att kunna göra kraftfulla saker med länkar på en sida, t.ex. öppna alla eller markerade i nya flikar.