I am using Fedora 24 with kde, so Theme Font & Size Changer is not supported. The kde application can surely be scaled by the system setting, but thunderbird do not follow the scaling. And the Preference -> Display -> Font setting can only change the font of the reading mail. In firefox, the situation is similar but it can be solve by changing the about:config -> layout.css.devPixelsPerPx value, though the font size of tab and menu bar don't change at all, it is okay as long as the website scale change. However, correcting the value in thunderbird only affect the layout but not the font size, the Inbox list words are nearly unreadable. Is there any way to solve the problem?