What is your anti-virus software?

Kinda usless asking this here as I wont be able to get the answer.

This is a web forum, not a mailing list.

Thanks Christ1 I have Kapersky but it ran out 2 weeks ago The internet (Firebird) is working fine as well as everything else just Thunderbird. I mentioned the email as Mozilla said I would get email notification when someone answered. Sorry I didnt mean to cause offence

Try to start Windows in safe mode with networking enabled. - Win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode - Win8 https://support.microsoft.com/en-us/help/17076/windows-8-startup-settings-safe-mode - Win7 https://support.microsoft.com/en-us/help/17419/windows-7-advanced-startup-options-safe-mode#start-computer-safe-mode=windows-7

Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/kb/safe-mode

Does the problem go away?

I couldnt start in safe mode but I used the link to start Thunderbird in safe mode and to disable the add ons. I can now delete and read emails. I am just wondering though do I need to do anything else? Your answer was very helpful thank you

I have to say that my current Firefox (I'm trialling 50.0) frequently stalls (goes pale and Windows says it isn't responding) and Thunderbird (50.0b3) occasionally does the same. That's here at work on Windows 7; I don't see this ever on my Linux systems at home.

I take it this is not a common problem or we'd be awash with complaints about it on this forum. I can't identify any particular action on my part that triggers it.

I've just noticed that I have hardware acceleration turned on in both programs (when did that happen?) so I'll turn it off and see what happens.

Zenos thats exactly what mine is doing. Starting in Safe Mode and disabling the add ons has helped though. I am Windows 7 as Windows 10 nearly had me in a mental asylum

Apart from muting all your add-ons and customizations, Safe Mode also disables hardware acceleration (which is about taking advantage of features of your display adapter). So that may just be what you need to check; is it enabled?

Tools|Options|Advanced|General|Advanced Configuration→"Use hardware acceleration when available"

I've turned mine off and am waiting to see what happens next…

Funnily enough, the program seems more responsive since doing so.