Just update. All of the largest mail providers are changing to some form of oauth authentication and your Thunderbird just does not support those protocols as implemented now. There are, and will not be, instructions for version 60. It went out of support some 5 years ago.

Theme and font size changer is, as you are aware obsolete, and has been for years. You do not need it, you just want it. Thunderbird has all the scaling settings you need built in an has had variations available for some years now with regard to density and font size. Although I note in your image that all of the settings are set to default, including scaling, so it is doing nothing anyway.

Matt. If the current verion of Thunderbird has all the font size changes NOW, that it did not have THEN, then great, I will upgrade, BUT don't tell me that "You do not need it, you just want it" and " it is doing nothing anyway".

This is just plain wrong and rude!

When I did my last upgrade, and I could not use the add-on, my font sizes went all wrong, and I could not change it back to any size I could read by any Thunderbird control, and I had to search how to put my version back to a previous version and re-install the add-on to get a screen that I could read. So I DID need it (even if most of controls are at default - without the add-on and the lastest version then, I could not read the fonts as they were too small).

I was not the only person to have this problem at the time, and solution (revert back to previos version) was posted on your own help forum.

I would appreciate if you would just answer questions as posed, and not add any of your own personal and rude comments.

Matt. If the current verion of Thunderbird has all the font size changes NOW, that it did not have THEN, then great, I will upgrade, BUT don't tell me that "You do not need it, you just want it" and " it is doing nothing anyway". This is just plain wrong and rude!

Ok I will bite. There is the image you posted. What exactly is it doing to adjust your settings? Everything is in it's default state. Ergo it is doing nothing.

Yes, most set to default, but as I said, when I last upgraded TB, font size went to pot. Only way to get reasonable sizes fonts was to downgrade TB to what I had previously and re-load the add-on. It was probably the add-on that enabled me to get good size fonts, not TB. The fact that I have 'default' and that satisfies what I want is irrelevant. I checked this out now by removing the add-on, and fonts went bad again. Re-installed add on and all back to how I want it (even if that happens to be default). So that is why kept old version of TB and the add-on. Thus I need it (with my old version of TB).

Now, If you say that TB has sorted out all it's font size problems that it had many years ago, necessitating someone creating an add on to solve the problems, I will give it a try..... but be prepared to get another message if it does not get me back to how it is at present.