Do you know much like  Firefox 3.6 Firefox 4.0 also shows thumbnail previews of tabs when we use Ctrl +Tab keys combination but this feature was disabled by default in Firefox 4.0 we can enable it easily.

ctrl tab previews in Firefox 4.0

Enable Ctrl +Tab previews in Firefox 4.0

1.Open Firefox 4.0 beta 1 browser, and type about:config in the address bar and click I’ll be careful, I promise

enable ctrltab previews

2.Now type previews  in filter and double click browser.ctrlTab.previews to set to true.

Now you can able to switch between thumbnail previews of opened tab using Ctrl+Tab in Firefox 4.0