Maybe you are jumping to conclusions because you are not asking how to increase the generic font size in the Thunderbird UI or perhaps you have not used the search to find solutions previously answered loads of times or not located some info in Help Articles.

If you are having an issue searching using eg: google or within the Mozilla Thunderbird Help Support Forum, it would be more helpful for yourself to ask for help stating the problem. Remember you are asking other Thunderbird users who freely volunteer help to assist people.

So I'm going to assume you need to increase generic font size.

When you post a question, you need to assume no one knows what Operating System you are using and no one knows what version of Thunderbird you are using, so always post that information because the answer you get may depend upon it.

If you are using 78* and Windows OS then you will find info under 'Options' If using 91* and Windows OS then 'Options' has been renamed to 'Preferences'.

• Menu icon > Options/Preferences > 'General'
• Scroll to the bottom
• click on 'Config Editor' button.

• You will see a friendly warning - accept the risk.
• In search type : pixels
• look for this line: layout.css.devPixelsPerPx

the default is a negative value: -1.0

If using 78*:

• double click on that line to open a small window OR right-click the preference and select 'Modify' which allows you to change the 'Value'
• You can try positive values such as 1.20 or 1.25 or 1.5
• click on 'OK'

If using 91*:

• click on the pencil icon to edit the value OR double click on line to open the edit
• You can try positive values such as 1.20 or 1.25 or 1.5
• click on the tick icon to save your entry.

You will instantly see an increase in font size, so you can modify the overall font size of the user interface to suit whatever you prefer. Note: if using a MAC then you may find you need to use higher numbers, but always start lower eg: 1.5, then 2.0 etc - use a higher number if required.

Hopefully this should help with the generic font size of the UI.

Once this is sorted then let me know if there is still an issue with font in emails received being too small on occasions as you may have not set a minimum font size in your settings.

I have looked through your previous questions and have discovered that you are up to date using version 91*

I've also read that you have already been instructed on what to do in order to increase the generic size of font in Thunderbird.

You mention a problem with dyslexia, so I've typed instructions again, but this time I've added a couple of images which might help you.

The following images may help if using 91*

• click on 'Menu app icon' - icon has 3 lines
• click on 'Preferences

First images shows what you see after selecting 'Preferences'

• click on 'General'
• Scroll to the bottom
• click on 'Config Editor' button.

• You will see a friendly warning - accept the risk.

Second image top half shows where to type and what to look for

• In search type : pixels
• look for this line: layout.css.devPixelsPerPx

the default is a negative value: -1.0

• click on the pencil icon to edit the value

Second image bottom half shows where to alter data and how to save it:

• You can try positive values such as 1.20 or 1.25 or 1.5 or 2.0
• click on the tick icon to save your entry.

Image shows I typed 1.5, but if too big then go back and try 1.25 Do not type larger than 2.0 because you may start to have other problems which can be fixed but are not so straight forward.

Too complicated. No other programmes are unreadable as they use my Windows default large, only thunderbirds has made almost all received emails font so tiny that I can no longer read them. I did try to follow previous instructions which made no difference.

You have been provided with instructions on how to do it. Either do it or not there is not another alternative available. If it is to complex for you, perhaps hire someone with the skills to undertake the actions described. Just as you would hire a motor mechanic for your car or a plumber to fix your drains once it exceeded your skill level.

The developers are looking at allowing users to set a font size here. But anything they come up with is probably about a year away from release.

The sizes of fonts used in messages themselves are generally set by the sender. To make them larger for reading use CTRL++ to zoom the message to a size you like. This is being discussed in this bug

Too complicated. No other programmes are unreadable as they use my Windows default large, only thunderbirds has made almost all received emails font so tiny that I can no longer read them. I did try to follow previous instructions which made no difference.

I have helped people with various levels of skill and many over 80 years old who felt intimated by going into areas that were not familiar, but when it comes to the information I supplied, they found it simple when they followed it one step at a time especially when I provided images so they could understand what it looked like.

If you really cannot follow those very clear simple instructions then you need to follow Matt's advise.

If it is to complex for you, perhaps hire someone with the skills to undertake the actions described. Just as you would hire a motor mechanic for your car or a plumber to fix your drains once it exceeded your skill level.

You can always show the person you choose to hire the information I provided, so they fix the problem within seconds.