Merge the address bar into the tabs' bar

[FernandoMMuniz]

1- Remove the dedicated address bar.
2- Move the remaining buttons up to the tabs' bar.
3- Make it so double-clicking the active tab causes it to expand across the whole tab bar, becoming an address bar.

Result: Now Firefox only have one obligatory bar, and the tabs are less likely to cause burn in than the address bar.

[Jon]

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