To only increase the font size in the 'Thread Pane' would require creation of 'userChrome.css' file and some code. I can supply all the information you would require. Just ask if this is really only what you want :) But, if you have a general need to increase font then you can use the following information and do it very quickly. * Menu app icon > Options * Select 'General' * Scroll down to the very bottom * click on 'Config Editor' button to open 'about:config' It will say be careful :) * In search type:''' pixels''' * Look for this line: '''layout.css.devPixelsPerPx''' * Double left click on that line to open the 'Enter string Value' box so you can edit the Value. The default value will be -1.0 * Enter a new number eg: 1.25 or 1.5 or 2.0 or 2.2 * click on OK the effect is immediate, so you can modify that number until it looks ok for you. I've included an image as a guide. It is from version 68.11.0, but all the about:config info is identical.