Correction to (2): In my particular case, my script had an @requires tag in the header. When greasemonkey/firefox (re)installed my script, it also installed the newer version of the required file, so that my state was changed even when I thought I was reverting to a previous state. The wiki troubleshooting page might reference the @requires tag associated with this particular symptom.
As discussed in another thread, the particular problem was that I was referencing an auto-updater script from "
swizzlemctwizzle.com", that domain is no longer in business, and the updater script no longer works.
1) Loading the script into Chrome may be a useful troubleshooting step. The chrome error message and debugging tools may provide errors that are not provided by greasemonkey/firefox tools. Chrome may display other interesting symptoms that can help debug a problem.
2) In my particular case, I had problems with updater.php. It may be desirable to mention updater.php in the troubleshooting page. Specifically, it was not immediately obvious to me that the error message I eventually found in my firefox error console referring to updater.php was relevant. The specific symptoms: a file works, but stops working when reloaded, may indicate a problem in updater.php. A pointer to more information about updater.php may be useful.