This is the one I'm using: https://github.com/Qeole/colorediffs https://github.com/Qeole/colorediffs. I installed it several years ago, so I'm not entirely sur

This is the one I'm using: https://github.com/Qeole/colorediffs https://github.com/Qeole/colorediffs. I installed it several years ago, so I'm not entirely sure whether you can install it on a current version of Thunderbird, but it is still working with my installation.