Time to switch to the new version Rated 1 out of 5 stars
For a long time TU was a must-have but it got abandoned and with recent updates it will begin to fail. The page says there is an update coming and that was written long ago. It is doubtful that it is ever going to happen.
There is a new version of it that works beautifully found here: https://addons.mozilla.org/en-us/firefox/addon/tab-utilities-phoenix/
If you run Palemoon you also will need to follow it's instructions and also get the Tab Groups add-on for it to fully function. When PM removed tab groups in version 24 it took some of TU's functionality with it. Even if you don't use tab groups just having the add-on will patch the broken functions.
Anyways, TU was great and Ithinc did a great job for a long time. Now it is time to switch to the updated version and be in tab heaven!