If you are having a general issue with reading on your computer, you could change the screen resolution to display everything much larger. 'Start' > 'Control Panel' > 'Personalization' > 'Display Settings'

The lower the number of pixels, the bigger the font. This effects everything, not just Thunderbird, so may be of benefit in general.

You could create a css file. This only effects Thunderbird. This may seem a little daunting, but it is simple. It requires you to be able to follow instructions, create folders, copy, paste and save files. You do not need to actually write code.

Make Hidden files and folder visible:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

In Thunderbird:

• Help > Troubleshooting Information
• click on 'Open folder' button

a new window opens showing contents of your Profile folder.

• Close Thunderbird now - this is important.

• Create new folder and call it chrome note the spelling - use a lower case 'c' . It should be in the same place as the 'Mail' folder. See image below as a guide to show where it should be.

• open Notepad

usually located under All Programs > Accessories > Notepad

• Copy all the text between lines below and paste it into the Notepad document.

An example image is below - you can edit to choose size.

/*
 
* Do not remove the @namespace line -- it's required for correct functioning
 */

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); 

/*
*Make all the default font sizes eg:14 px:
*/

   * { font-size: 14px !important; } 

If this proves to be too small you can edit the 14px to say 16px etc

• Save the document as filename userChrome.css in the chrome folder. Note the spelling all lower case except for the 'C'. See image below.

• Restart Thunderbird.

Thanks. Your answer completely solved my problems. It even gave me a way to increase the size of the text in the future as my eyesight weakens even more. Kudos to you. Thanks a lot.

Good to hear Thunderbird is now offering a better visibility for you.

I am using Tbird on a linux ubuntu-based OS.

Open Folder is replaced by Open Directory, which doesn't work, just opens Audacious music player! Maybe it's a linux thing, I might ask on a linux forum. (note, on same OS, Firefox>troubleshooting does give the file location).

There is the Font Changer add-on, but if installed it has access to all data, hardly an enhancement to privacy!

A pity the default font size for inbox, folders, is so small. It takes away from a terrific desktop appl.

Incidentally it is easy to zoom individual emails, so no problem there.

linuxuser23 re:There is the Font Changer add-on, but if installed it has access to all data, hardly an enhancement to privacy!

It's got nothing to do with privacy and everything to do with changing font size in all the various sections to do with font size :)

re:Open Folder is replaced by Open Directory, which doesn't work, just opens Audacious music player! Profile location: http://kb.mozillazine.org/Profile_folder_-_Thunderbird#Linux_and_Unix You can use info here to access the 'profile name' folder.

Are you using latest version of Thunderbird? Latest version is 52.8.0 This is the official download: https://www.thunderbird.net/en-US/thunderbird/all/

Please note this question has been marked as solved. When you post a comment, it is being sent to original postee of question. The original poster of question may not be able to assist especially as you do not use the same OS or may not appreciate receiving emails that have nothing to do with them. It would be better for you if you posted your own question then anyone who helps on the forum will see it. I only saw it because I failed to stop following a solved question.

I have 52.8.0.

Thank you for link to mozillazine, I will look there.

However, re: 'It's got nothing to do with privacy and everything to do with changing font size in all the various sections to do with font size :)'

I fail to see how there is no privacy issue if some site wanhunglo.com are given access to all my data on Tbird. Who are they? And the tone of your dismissal seems a bit arrogant!

linuxuser23 Addon extensions are not part of Thunderbird. They are created by people who have the ownership and responsibility of the addon. You can choose to use them; it is not obligatory.

There is an alternative to using an addon. I added the additional useful information of how to alter some fonts in Thunderbird yourself without the need for addons. It was selected as the 'chosen solution'. As you have selected to comment in this other persons question, I would have expected you to have used that 'Chosen Solution' to see if worked for you.

This 'Chosen Solution' has nothing to do with other peoples addon extensions.

re: wanhunglo.com. I presume you have downloaded the addon 'Theme Font and Size Changer (fixed)' 64.3 created by Bzzz which lists the authors homepage as: http://www.wanhunglo.com/2018/theme-font-size-changer-for-thunderbird-e6

The other version is the 'Theme Font and Size Changer for Thunderbird' 64.1 by Baris Derin Homepage: https://barisderin.com/?p=286

Both of these websites have their own 'Privacy Policy' statements.

Hi ,
You're replying to a thread that is old. You should use https://support.mozilla.org/en-US/questions/new where volunteers can get more details about your setup.

Because this thread is old and more people might start using it for their own questions, I'm going to lock it.