After automated update to Thunderbird 91 from the 7x version, running Windows 10, was trying to return to the pre-version 91 ATTACH file display that had the files listed vertically to the upper right corner of the screen, instead of the current horizontal display at the bottom of the page. Then I accidentally did a very bad thing. I right clicked in the space near the ATTACH icon on the upper right corner of the screen. I then unclicked the check mark on what was probably the second entry of the list of what I think was four choices, which I thought was ATTACH related. What it did instead was to entirely remove the ATTACH icon. Even worse, it removed the SEND icon. I can now compose emails, but cannot attach any files. Or worse, I cannot send the composed email to anyone! I have taken screenshots of my Write email screen and my Main screen of Thunderbird. You can see these at https://heart-test.com/thunderbird/ where you see the .jpg versions of these screens, or you can also see .bmp or .png formats if you prefer. I'd appreciate any assistance you could provide, since I cannot send any email at the moment. Please email me at stan@coeh.com or DrH@coeh.com as those will get my immediate attention. If you would like to have me call you, please email me a phone number to call. Thanks for your assistance. Stan (Note: I had to upload the screenshots this way since "Add Images" icon on this website just gives me a "spinning circle" graphic but does not finish.)