I would like to have the menu above the Get Messages ribbon, as it was in older versions of Thunderbird. I find the current arrangement difficult to use.
- skip 'Enable userChrome customization in about:config'; you've already done that
- follow the instructions under 'Locate and open your profile folder..' Note: for TB, the menu choice is Help > Troubleshooting Information.
- follow the instructions under 'Create the folder and its files' (make sure userChrome.css doesn't end with .txt - Windows must be set not to hide extensions for known file types)
- once userChrome.css is created, open it and enter the code I mentioned above
- save the file > ignore the rest of the instructions > restart TB