"Direct download" will place it into your downloads folder. Then these instructions can help you install it.

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

A regular contributor to the newsgroup has also prepared a version:

http://www.rossde.com/ThemeFontSizeChangerNoexpire/index.html

Zenos said

"Direct download" will place it into your downloads folder. Then these instructions can help you install it. https://support.mozilla.org/en-US/kb/installing-addon-thunderbird A regular contributor to the newsgroup has also prepared a version: http://www.rossde.com/ThemeFontSizeChangerNoexpire/index.html

EUREAKA!!! It worked - Thank you VERY much! Now, how do I prevent it from going missing again (as it has done several times before)??

Thank You!

Thank You!

Hi, I've used the above link addon and it was disabled at next boot of Thunderbird v52.5.2.

I heard about a CSS file to modify the TB aspect, but I cannot find any reference to that.

Anyone has any clue about how to make bigger the system font of TB, I'm open to chat and look for a solution, the current font is too small and so difficult to read, the messages and the interface itself.

Thanks in advance. Cayetano H. Osma

Here is a description of how to do it using the css file:

https://support.mozilla.org/en-US/questions/1198055#answer-1059555

Further down is another suggestion about doing it via the Config Editor:

https://support.mozilla.org/en-US/questions/1198055?page=2#answer-1062172

…and yet another approach, on the same lines, discusses changing this parameter:

layout.css.dpi

There are several links floating about, but I recommend not using the rossde.com one, but instead the one given here. Remove whatever Theme Font add-on you have in Tools/Add-ons/Extensions, restart TB, then drag the downloaded xpi file from wherever you saved it and drop it onto Tools/Add-ons/Extensions to install the modified add-on.

The link & instructions previously provided by Zenos worked as I previously indicated and gave my thanks for.

I've resolved the issue installing the modified add-on from http://www.rossde.com/ThemeFontSizeChangerNoexpire/index.html

Testing and working on TB 52.5.2 (64-bit) on Mac OS X Sierra

Thanks to SH, Sfhowes and Zenos.

Regards, Cayetano H. Osma

TF&SC 64.1 for TB now available:

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

Tested and working in TB 52.5.2, not working in TB 58b3.

sfhowes said

TF&SC 64.1 for TB now available: https://addons.mozilla.org/en-us/thunderbird/addon/theme-font-size-changer-for-tb/ Tested and working in TB 52.5.2, not working in TB 58b3.

I do we now if there is or isn't an expiration date embedded as with the last version?

The new version still contains the 'time bomb' line that my earlier post recommended be commented out, so at some time it will probably expire, based on the new version's build number. If a follow-on version is not released before the current one expires, I presume the commenting fix will work as before.

sfhowes said

The new version still contains the 'time bomb' line that my earlier post recommended be commented out, so at some time it will probably expire, based on the new version's build number. If a follow-on version is not released before the current one expires, I presume the commenting fix will work as before.

I think I stick with the modified version you supplied the link for - it's working. And as the saying goes - "if it ain't brook, don't fix it"