If you have a general issue with the UI: Have a look at this addon: * https://addons.mozilla.org/en-US/thunderbird/addon/theme-font-size-changer/ In order to install a downloaded extension, please do the following: #Click the menu button [[Image:New Fx Menu]] and choose Add-ons. #Drag your downloaded XPI file to the Add-ons Manager tab and drop it. or #Click the menu button [[Image:New Fx Menu]] and choose Add-ons. #Click the gear icon at the top-right corner to the left of the search box and select ''Install Add-on From File…'' #Locate the XPI file you downloaded and click ''Open''. #You may need to restart Thunderbird when prompted. For more detailed instructions and information about installing add-ons, see [[Installing an Add-on in Thunderbird]].