What's worse is when you have enough tabs open, they start becoming hidden under the open-new-tab button on the right. This has been a bug for a long time. I suspect it's gotten tied up with the furor over the removal of the side/vertical tabs, which have been hacked in via addons since. What's sad is that Firefox already has an elegant solution -- maintain a minimum useful tab width and enable horizontal scrolling of the tab row when the mouse is over it.