Tabs Always in Titlebar Rated 5 out of 5 stars

Excellent add-on.
I found a fix for when a popup window opens, causing the the tabs to shift left over the Firefox menu button:

First, you need to set new windows to open in a new tab in the Firefox options.

Second, in about:config, change the value to 0.

This review is for a previous version of the add-on (