https://addons.mozill...firefox/addon/162063/
Theme Font Size Changer doesn't change the text within web pages (there are settings to do that) but instead changes the font size in all menus, toolbars, etc within Firefox itself without having to use a different theme (although there is the possibility of conflict with some non-default themes).
For example, I use the LittleFox theme for which the toolbars and tab headings are narrow; it increases the amount of the screen used for displaying a web page - it's only a little but I appreciate it. But the one downside is that the text on menus is also small (font size 9) and I have to admit to sometimes needing to get closer to the screen just to read them. Using this add-on I can increase the font size temporarily to do just that and shrink it back down to normal when I have finished.
So for anyone who has trouble reading the menus or tab headings, things like that, but doesn't want to change the browser theme then this is a simple to use extension that may be very handy.
(I realise that this isn't a question but thought that the add-on might be useful to some users)