[more-compact-tabs.css] compact buttons in tab bar

[Glandos]

If some buttons are located in the tab bar, they extend it to 27px. Buttons can come from extension, or Firefox itself (with the "all-tabs" dropdown). This patch should avoid the vertical expansion.

[Timvde]

Sorry for the late reply. By now, it doesn't seem to work at all anymore :( See #99. Would you mind looking into this? I promise to reply quicker :)