Firefox customization shenanigans

It's 2014-04-30, and I'm admiring the new look of Firefox. I notice that its toolbars have changed, so I decide to customize them, to remove redundant items and generally re-organize. But it's all wrong!

• How do I add a separator? I tried removing one, but it didn't re-appear in the available icons.

• How do I add stretching space? I daren't try to remove the current one in case I can't get it back again.

• How do I create a new toolbar?

• The damn thing has resized my window because the customization features are no longer in an external window but a new tab. Leave my window size alone!