Select Help/Restart with Add-ons Disabled (safe mode); any difference?

Thanks for getting back to me with this suggestion. When I do as you suggest and open TB in safe mode with add-ons disabled the issue is resolved. However, when I log out and log back in again as normal, the problem of not being able to write in the new email or reply window returns and I have to go through the safe mode process again. Is there any way I can disable add-ons - as that seems to be the issue - on a permanent basis?

If the problem is due to add-ons, open Tools/Add-ons/Extensions and disable the add-ons, if any, one at a time, and restart. Keep doing this until you find the add-on that is causing the problem. Also, use the default theme if not already doing so.

If an add-on or theme isn't a factor, the next possibility is a broken layout. Launch in safe mode, check 'Reset toolbars and controls', then click 'Make changes and restart'.

Report back if none of these methods work.

Thanks very much for your help. Your suggestion worked after I disabled shockwave flash plug-in. For info, I didn't have any extensions and was using the default theme, so I suspect the shockwave flash was the culprit.