have you disabled your addons? sounds like one of them has issues if everything is ok in troubleshooting mode.

Thanks for the reply but I have tried all that to no effect. On opening Thunderbird initially I get a brief blue flash across the top of the viewing pane on clicking the first email in the list thereafter nothing whichever mail I click and thus have to revert to Troubleshoot mode.

In normal mode, uncheck the box for hardware acceleration in Preferences/General/Indexing (it is disabled in safe mode). Then launch again in safe/troubleshoot mode, 'Reset toolbars & controls', 'Make changes & restart'.

Many thanks for the comprehensive reply but regrettably the problem remains after 3 attempts just to make sure I was getting it right.

Safe mode disables all add-ons, uses the default layout and theme, disables hardware acceleration, plus a few other less-common features. Make sure you've applied all suggestions, including removing language packs if you have any. If it still doesn't work in normal mode, try with a new profile created from Help/More Troubleshooting, about:profiles. The current profile is unaffected.

Double checked all the settings as recommended and still no joy so as advised set up a new profile and problem solved!

Many thanks for your assistance.