Tab Utilities is a great add-on. I normally don't contribute to sites (the reason is they can make bad judgements like Microsoft and Mozilla Firefox), but, in the past, I did with Tab Utilities. This shows in my books it a great add-on, and I hope they continue to be so.
The problem is that some programs, like Microsoft and Mozilla Firefox has lost sight of the users and their desires, and are now in business for themselves; which is a death knell for any business.
Microsoft with version 7 deleted some features that were in X P version that upset many people. Such as being able to place pictures in a certain order that one desires. This they deleted. They, also, took away the ability to have animated pictures (like the planets of the solar system orbiting around the sun, or 2 stars orbiting each other) (these 2 things are necessary and great for photographers and scientists). Then they added to it with version 8, where those that I know who are military computer experts (way above my level) have said that one almost needs to learn a new system to run, and irritated many of them.
With Firefox, after version 28, they ceased to listen to the users of their program (or at least seems to have). Many liked the option of choosing where the (work) tab bar would be; with most desiring it right on top of the window. However, Firefox has made it so that it is clear at the top, over the location bar (where you type in the addresses). This a great deal of people dislike; especially in the past Firefox gave them the option of where they wanted it. Also, the star (favorites) that was in the location bar they placed outside the location bar and the color at the top is such that it masks the names in the tabs making them hard to read. Both of these, also, upsets people with Firefox. All these to some degree can be corrected by an add-on (it still doesn't look quite right, but it will do). This add-on has some minor compatibility issues with Tab Utilities and causes some minor problems.
Many people have been posting many negative comments on Firefox on the internet and in Firefox feedback area. Yet, Firefox has not deemed to include this things in the new versions, as they did and could again. And because of this many are leaving Firefox for other browsers.
I have had people that I, in the past, introduced to Firefox, who have become dissatisfied with Firefox who advised me to leave Firefox as they have, and get a different browser. Some, are not downloading the new versions, but are keeping an older version.
Now I have seen in Firefox version 37.0.1 and 37.0.2 that when you install these versions, during a compatibility check, they tell you they are disabling Tab Utilities due to compatibility issues and that there is no newer versions available.
The problem lies with Firefox, who have lost touch with the customer and their desires, and are self-serving.
I, and others, can only hope for 2 things: 1. Firefox will start listening to their users and adjust their program's new version to their desires. 2. That Tab Utilities will come up with a new version that is compatible with Firefox's new versions, and, yet, will maintain the quality of the program that people love and use.