Can you provide the name of the old addon. I am not able to ascertain what a drop down box editor is.

Hi, Last used was Menu Wizard 5.10

As mentioned in the description all addons that used to modify UI using XUL have been deprecated. But it is still possible to use userChrome.css and userContent.css for customizing the UI and pages in Firefox, see http://kb.mozillazine.org/index.php?title=UserChrome.css&printable=yes and https://www.userchrome.org/

Thanks for taking time to reply, I'll get someone a little more competent than me to try that.

Here are some userChrome CSS resources that you might find helpful: https://www.userchrome.org/ https://www.reddit.com/r/FirefoxCSS/ https://github.com/Aris-t2/CustomCSSforFx