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First thing to try is run in safe/troubleshoot mode (hold Shift when launching TB). This mode applies the default layout, disables add-ons, applies the default theme and disables hardware acceleration (in Preferences/General), among other things.

I did as you suggested and it opened in the correct format but when I closed that down and reopened as usual it was back to the dis-jointed type. Is there anyway I can save the original formatting? I am 77 years old and not all that good on computers and no younger friends or neighbours around to call on so I really appreciate your help as I love using Thunderbird. Thanks

Launch in normal mode, uncheck the hardware acceleration box in Preferences/General (bottom of page). Restart in normal mode. If the display is still bad, close TB and launch in safe mode, check 'Reset toolbars & controls', 'Make changes & restart'. Reply here if the display is still not correct.

Thanks for your prompt reply. I launched in normal mode but all that comes up is my emails at the top of the page and a "Welcome to Thunderbird" asking about donations, Get Involved, Get Support, Report a Bug. I cannot find anything about Preferences/General at the bottom of the page. I re-launched in safe mode and checked the "reset toolbars and controls" and "Make changes and restart" but nothing had changed and still not getting the correct display?

Thank you so much for your patience - yes, it worked, I'm most grateful.