If the menu bar is missing right click on the toolbar and select Menu Bar in the list box.Delete it per the instructions in the preceding paragraph. If every time you close the message pane it re-opens when you restart, xulstore.json is probably corrupt.Xulstore.json replaced localstore.rdf in one of the updates to version 38. If you don't have a xulstore.json file, delete localstore.rdf instead. That will create a new version of that file with default settings. That stores the toolbar, window layout and size/position settings. Exit Thunderbird and delete xulstore.json. It will display the contents of your profile. That will launch windows explorer (or whatever file manager your operating system uses). Depending upon what version you are running you will see either a 'Open Containing Folder' or a 'Show Folder' button. If that doesn't help select Help -> Troubleshooting Information.If you are using the CompactHeader add-on for the message pane (preview pane) you many need to either expand the headers or disable the add-on in order to customize that toolbar. Right click on the 'broken' toolbar, select 'customize', press the 'Restore Default Set' button, and press the Done button.If the Mail or Message Pane toolbar doesn't seem to work correctly (for example, can't add or delete buttons):.This article was written for Thunderbird but also applies to Mozilla Suite / SeaMonkey (though some menu sequences may differ).

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