My favourite feature of Taskbar previews is hidden by default in Firefox. You can enable it. I do know why this feature has been disabled by default.
You need to download latest Firefox
Install it,launch it.
- In the URL field type: about:config
- You may see a warning click the I’ll be careful,I promise!
- In the Filter field type: browser.taskbar.previews.enable
- Doube click the browser.taskbar.previews.enable field and the value will toggle to True
Now you will see the previews