Another feature "borrowed" from another browser :)

In Google Chrome, when you open or close tabs, they will smoothly slide into or out of view. It's a neat little piece of eye candy and people tend to love it. Consequently, there is an addon that implements animations for opening and closing tabs in Firefox. The author states that he was inspired by a feature planned for Firefox 4 - tab animations.

And indeed, the feature has recently landed on trunk and already works with recent nigthly builds of Firefox 4, but since it is a new and experimental feature, it is disabled by default and there is no option for it. As always, about:config will be more than happy to help :)

Look for browser.tabs.animate and set it to true. If the setting does - for whatever reason - not yet exist in your profile, create a new Boolean value and set it to true. A restart of Firefox is required after changing this setting.

You need to have a very recent nightly version of Firefox 4. If it doesn't work after adding the value in about:config, your version is probably too old. Get a newer one.

One warning though

There is one issue which will result in "ghost tabs" - when you close a tab, it will lose its label, icon and close button, but the tab outline will remain on the tab strip. This happens when you have modified your maximum tab width (here is an article that tells you how to do this) which apparently confuses the animation code. Just make sure to NOT use a modified maximum tab width and all should be fine. The bug is not triggered when only changing the minimum tab width.