You cannot disable the main functions on a program.

To make the sort correct you simply have to reclick on the 'Date' header. If it shows oldest at top, click on it again to put newest on top.

I do understand your situation as I also have a 92 year old father using emails etc. It is not so easy manoeuvring a mouse for older or less experienced people or anyone with hand coordinating/manipulating difficulties.

Things you can do to help make life easier.

Increase the font size to make the target much bigger. Use this addon to do this:

• https://addons.mozilla.org/en-us/thunderbird/addon/theme-font-size-changer/

If you are using a laptop, some people find it hard to control the mousepad, you could try a couple of things.

Make the mousepad less sensitive. Do this via the Control Panel on your computer.

Purchase a suitable mouse which can be used with the laptop and fits her hand comfortably. The mouse can also have the sensitivity decreased via the Control Panel > Mouse

There is actually an add-on that includes a 'Column heading lock' option to do exactly what you want.

http://mailtweak.mozdev.org/tweaks.html#columnlock

Tested and working here in TB 24 & 31.

http://chrisramsden.vfast.co.uk/3_How_to_install_Add-ons_in_Thunderbird.html

I tried installing mailtweak-1.0pre10.xpi add-on but it said it's not compatible with Thunderbird 24.5.0. I wonder if there's a compatible version? It sounds perfect for my 92 year old mother!

Download and install this add-on:

https://addons.mozilla.org/en-US/thunderbird/addon/checkcompatibility/

then you should be able to install mailtweak. You may still see a warning on the Extensions page that it's incompatible with TB 24.5, but that won't stop it from working.

Thanks to everyone. The checkcompatibility add-on allowed me to install mailtweak. My 92 year old mother will sure appreciate all your help!

Cheapest Mothers' Day gift ever...