Alternatives to and/or Updates to Theme and Font Changer?

Hi All – For new Thunderbird version 68.4.1 the Theme and Font Changer add-on is no longer compatible. I see that it has not been updated since 2018. This is a big problem for those of us needing new glasses as the font is too small and color contrasts too minimal without add-on assistance.

Does anyone have good alternative add-ons that work with version 68.4.1?

Updates on the likelihood of Theme and Font Changer being updated to be compatible?



It’s clear from the support page of Theme Font & Size Changer that the author is not going to update this for TB68 (due to underlying changes in TB). And even if he did it would not survive long because this type of addon will not work at all in future.

It could be that in future (TB78+) someone might write an similar addon. But for now I think you’ll have to fall back to what TB itself provides in its preferences and, if that’s insufficient, a technology known as ‘useChrome.css’ - which has existed since the last century to modify sizes and colours on Firefox and Thunderbird - and still works to some extent. Unfortunately it’s a rather techie method - involving inserting files into your Thunderbird profile.

So, I suggest you forget addons for now and raise this as a question on the Thunderbird User Support site What exactly do you want - contrast and font sizes where - e.g. the compose window, the lists of emails, the buttons…?

See this recent question where both preferences and userChrome was suggested to solve a possibly similar question.

Good luck.



Thank you very much for the highly useful and direct advice on how to proceed. I am looking through these options. Appreciated.

I’m sure there are very good reasons for the changes, but kind of frustrating from an end user perspective!

I used to be more technical, I will put that hat on again and see what I can manage.


Hi there Michael and DaveRo,

It would be good to provide step by step instructions for the tech dunces like me if you find a work around. I use a mac and the font in the message list is way too small. All attempts to change the font only affect the message content not the message list, which i need to be able to visually scan without missing messages from important contacts.
I’ve been using Thunderbird for years and dont particularly want to try and transfer all my folders with different colour coding for different tags on particular emails to another program. I’m bound to lose something, such as tag colours, if I do.



OK, so for dunces like me on mac, I have pulled together from a few threads what worked for me (I use a mac OS10.10.5 but I don’t think the mac OS will make a difference?) in case anyone else on mac stumbles on this thread.

(All I wanted to do was increase the font size in the email list pane of the inbox so that i can visually scan the list for important emails.)

In Thunderbird, go to Preferences/Advanced/General/Config. editor

Accept the responsibility for armageddon when the pop-up asks you (but the pane needs to be sized large enough to allow you to see the continue button in the popup, which it wasn’t the first couple of times I tried. For some reason it wont load the button in the popup if the pane is too small so you can’t scroll down to it unless you click when the pane is already larger)

Scroll down the list to layout.css.devPixelsPerPx

Double click that line to open the editor popup and change from the default (-1.0) to 1.1 (but others in different posts have preferred 1.2, 1.25, 2 and even 4. Start at 1.0 or 1.1 if you are worried it might be too big, and that is with no negative sign.)