"New tab" button after last tab isn't visible in Firefox 29+

[Infocatcher]

We always have #tabbrowser-tabs[overflow="true"] even for only one opened tab.
And therefore "New tab" button is displayed at the end of tab bar (oh, this is original one because there is two buttons: movable on toolbar and yet another after las tab).

[Infocatcher]

Oops, this is conflict with Private Tab with fixes for Infocatcher/Private_Tab#137 (and all works fine with extensions.privateTab.fixAfterTabsButtonsAccessibility = false) :(

[Infocatcher]

Now this fix should be disabled for vertical tab bar. It shouldn't be needed in this case anyway. But this bug is very strange though.

[Infocatcher]

But this bug is very strange though.

Oh, I forgot about button's padding, should be better now: Infocatcher/Private_Tab@9e4a255

[Infocatcher]

Summary
This is only my fault: I set too big horizontal padding to .tabs-newtab-button > .toolbarbutton-icon and #tabbrowser-tabs[overflow="true"] appears as a result of horizontal overflow.