try the latest dev-build
That dev build seems to be much better, especially about the peekaboo gap between the tabs and the arrows. The only remaining issue seems to be when middle clicking a link on the bookmarks bar when the selected tab is right most and it is the last one. The new tab gets created, but it's hidden off-screen to the right of the current tab. The desired behaviour would be for the tabs to scroll left, leaving the current tab active (as is the current case) and show the newly-created tab to its right.
Otherwise, I continue to be appreciative of this add-in.