Web site editor errors on paste using Firefox

Recently we ran into a glitch using an online editor in a website CMS with the Firefox browser. Every time we tried to paste plain text into the editor, the editor would crash or display an error message. Other browsers worked fine (chromium, SeaMonkey), and Firefox worked fine on other workstations. It turns out it was the method some online editors use to process clipboard events. In 'about:config' the offending browser had

dom.event.clipboardevents.enabled

set to 'false'. Resetting to 'true' fixed the issue (the default setting). I had probably set this, or some no longer in use add-on/extension had set it, to enforce additional security or privacy.