In Windows. (I know I can open
Desktop > Properties > Appearance > Advanced > [and figure out which item determines it; probably
Menu]. But, I don't want other things changed - just the bookmarks. This is because I have so many and I want more of them to display.
I did see the question on changing font size of items in folder, on bookmarks toolbar, and sub-folders, etc; But, I'm talking sidebar on firefox, I don't have Google Chrome and I am not a developer.