Invalid Tab cannot be moved to a different Category

[RealRaven2000]

I am trying to remove (but keep) a Tab of an invalid OWL installation by selecting "QuickFolders Commands >> Remove from CUrrent Category" - the tab remains visible on screen and cannot be filtered out by changing to another Category.

In error console IU can see the following error log:

QuickFolders 12:39:38.466  [1472 ms]   
 TypeError: this.folder is null
    setSelectedCategory chrome://quickfolders/content/quickfolders-folder-category-dlg.js:129
    init chrome://quickfolders/content/quickfolders-folder-category-dlg.js:42
    _fireButtonEvent chrome://global/content/elements/dialog.js:495
    _doButtonCommand chrome://global/content/elements/dialog.js:474
    _handleButtonCommand chrome://global/content/elements/dialog.js:468
quickfolders-util.js:1262:13