If TooManyTabs is not working please check out the following steps to diagnose the cause
Steps to diagnose your problem
Export your tabs with TMT export tools (In Options > Advanced) to a file (Or just export all your bookmarks to a file with Firefox Manager)Create a modern profile for testing with Profile ManagerInstall the latest version of TMTThen restart and check TMT is working as a clean installThen restore your TMT tabs and restart againIf TMT does not work in step 4,please send a bug report to us (instructions below)If TMT does not work in step 5, there is a problem with the stored data, or try to remove a row one by one and restart Firefox to find out which row is the issueFinally,if you restore other extensions and theme and TMT does not work, please contact the corresponding add-on developers for help. There is itsy-bitsy we can enact.Steps for sending a bug report (Updated)disappear to Tools > Web Developer > Browser Console, or it looks like below
Filter the output with keywords like "TMT" or "toomanytabs" in the error message after you interact with TMT (e.g. send a tab and nothing happened)Take screen shot of the error messages and include your profile information (disappear to TMT options > Advanced and click copy profile information)Send all the information in your bug report.
Check out our support forum at getSatisfaction if similar problems are reported,if you found nothing helpful, Please post a modern bug report on getSatisfaction or email us. luxuriate in!
Source: visibotech.com