[garciansmith]

It means the content of two tabs is side by side but nothing else like the browser chrome. Haven't used this in Firefox yet, but I certainly find it useful for other apps like file browsers.

[hollandheese]

Huh? There's actually more stuff in the way than if you used two windows since the divider is actually larger than the gap between windows is.

The only way this saves on space is if you're using vertical tabs.

[orphea]

Whatever? I too prefer two windows side by side and I don't see this feature useful, but if others do, that's great.