I have not seen any change in either Thunderbird or Firefox to support your assertion that either of them had been optimised in any way for any particular size or quality of screen.

But then, I know how to set them both to use fonts and sizes to my liking. So even if the default had changed, it is easy and possible to override it.

My argument with both Firefox and Thunderbird would be with their choice of grey icons. As soon as you start using addons that bring coloured icons, the native grey ones look disabled or deactivated. And for that reason alone I'd go in search of a theme that restores colourful icons.

Past versions of Thunderbird are available here:

https://ftp.mozilla.org/pub/thunderbird/releases/

... so yes you can revert to an older version. But I don't see any need to do this if your argument is just about cosmetic changes; these are all adjustable.

Thank you! I didn't assert that the new update for Tb would do anything, only that that was my interpretation of an update note. I am happy that I was mistaken.

A huge change was made in the Ff GUI with v.29, which optimised it for small screens. It created a tsunami of large screen user complaints, though that didn't seem to concern the developers; they seemed impervious to the pleas of the peons. The change became reversable with the advent of the Classic Theme Restorer add-on. Only then did I install v. 29. From the wording of the Tb update note I feared a similar development for Tb. I am delighted that this is not the case.

My computer is set up so that I can operate in user mode, and get a pop-up for the admn password when I want to install something. This does not seem to work for the most recent update. Why? I have never before had switch to the admin account to update Tb.

"A huge change was made in the Ff GUI with v.29, which optimised it for small screens." That one passed me by. I'm using a beta, Fx50b7 IIRC, and haven't suffered this problem.

We do have complaints from users with hi-res screens, usually in that assorted text is too small. Most of these users rely on the Theme Font & Size Changer add-on to fix the menus etc. But that seems to me to be slowness in Thunderbird's development in reacting to advances in technology, rather than a sea change in its own design that makes it no longer work.

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

A rather more effective approach, I think, is to tweak the userContent.css and userChrome.css files to set font sizes.

Thank you for the link.

Ff v.29 was a long time ago. It eliminated control tabs that "crowded" small screens. This is what I regard as optimisation for small screens. The problem for big screens, which had plenty of room for the deleted control tabs, is that it took two clicks to accomplish what one used to do. Which I regard as de-optimisation for large screens. It was not an issue of font size, but the removal of useful control tabs.

I installed Tb 45.4, and as promised, no changes in the UI.

Thank you for your help.

This time I did not get the ususal problem solved option. The problem is solved. Thank you.