I've been getting the "A script on this page may be busy....." etc. pop up message consistently for over a week. The "continue" had been working until today, when everything completely stopped on gmail. I've cleaned up my computer, checked for latest Firefox upgrade, reset Firefox, and now was finally attempting to use the Firefox fix attempt: about:config and when I got to dom.max_script_run_time and tried to click and choose "reset" it was gray and not allowed to select.