I am now using Waterfox so that I can use my Firefox add ons. My eyesight is poor now and theme font & size changer is essential for me. However since yesterday I have tried all the versions to download and then turned off automatic updates. The icon is showing in the toolbar, but the problem I have is that when I open the theme font context menu it is not showing any fonts and every time I click on anything it comes up with a box showing Javascript Application TypeError:.

I don't if anyone has any idea what the problem is as without this add on I am going to really struggle to use the internet.