It's a useful extension, but will always stop working. It must be fixed by turn off and on. ********************* May be from these, Auto Tab Discard https://addons.mozilla.org/en-US/firefox/addon/auto-tab-discard/ Sleep Mode https://addons.mozilla.org/en-US/firefox/addon/sleep-mode/
Could you provide more information about the error? Any information in the browser console? Perhaps there is an incompatible with other add-ons you have installed.
