If you are using Firefox this is the way to fix it. A manifest will embed itself in your firefox folder for reasons I don’t know. But go to C:/program files/mozilla firefox/chrome. if you see a file called m3ffxtbr.manifest go ahead and delete it. It does no damage to the functionality of firefox and completely restores your stumble toolbar"
m3ffxtbr.manifest is apparently an installer for MyWebSearch toolbar for Firefox, and seems to cause a lot of problems with different addons.
If it still doesn't show, or that file isn't there, uninstall all addons, then reinstall SU, making sure you use the latest addon at https://addons.mozilla.org/en-US/firefox/addon/138?id=138
If I could be of further assistance, let me know. If this helps or solves the issue, please rate it.