How I can delete borders?

[Usergit358]

How I can delete spaces of frame? Please see picture. Thank you

[sputnik1]

In addition to extra space (even more space when setting checked in options), can't change width of tab bar. No symbol (usually double headed arrow ) to drag width of tab bar pops up on inside edge. I'm using FF 40.0.3 on Windows 7. Thanks for developing and maintaining this brilliant add-on.