Untested fix for the changes from bug 1273094

[gijsk]

I think this will do the 'right thing' both with and without the patches in bug 1273094, but I'm not in a good position to test the change.

See also https://github.com/darrinhenein/VerticalTabs/pull/37 .

[eoger]

Works for me, the double-click opens a new tab and the titlebar is the normal size again 👍