This is just an awesome feature Firefox has included with the latest version.
I dunno if any other browser has it, but I found it so interesting I should post about it.
By adding tab groups and putting different tabs in each group, each group will act as a new window, without a new window.
For example, a youtube playlist that is set on auto play and shuffle can be played in the background..without a new window or the tab even displayed.
Just love this feature.
If it's old, than I just recently discovered it. Felt like sharing it.