'''It is [[Install an older version of Firefox|NOT]] recommended to use old versions.''' Please be aware old versions of Firefox are insecure and unsafe. You may lose data, personal identity information &|or damage your machine if used whilst connected to the internet. I usually have multiple versions of Firefox installed, but not currently on this machine. So I can't right now just fire up an old version to check. Although this site does not document fully using older versions of Firefox, and actively cautions against doing so, I will post information because in addition to research reasons it is sometimes a valuable troubleshooting method. *Main important note is not to use the ''about:firefox'' option including viewing the info from the help menu because that triggers an update. *Early versions have an option in the settings to not update Firefox, so use that. * It is actually possible to stop an update, after you trigger one, as long as you act before restarting Fx. ** See old article [[Updates reported when running newest version#w_delete-update-configuration-files]]''_delete-update-configuration-files'' ** Delete hidden files "active-update.xml", "updates.xml", from the correct "updates" folder ** The tip to delete files is still accurate. but the article was automatically updated to mention the three bar icon menu button obviously not present in older versions of Firefox ** See also http://kb.mozillazine.org/Software_Update#Software_Update_not_working_properly * It is a good tip to retain the installer locally so if you do update you can easily reinstall. Use official versions as mentioned in [[Install an older version of Firefox]] Note it is good practice and near enough '''essential to use separate Firefox profiles''' for each version of Firefox that you use, and the custom install option will usually be needed to separate the program files of the Release and the old version. * http://kb.mozillazine.org/Testing_pre-release_versions#Installing_multiple_versions *[[Use the Profile Manager to create and remove Firefox profiles]] Good luck with your research. Please post back to say how you got on with installing the Firefox version you needed for research.

If you need such a old vulnerable version (released back on December 20th, 2011) for just one thing then consider using Firefox 9.0.1 portable since you have Windows. This will not touch any normal Firefox installs or settings. http://sourceforge.net/projects/portableapps/files/Mozilla%20Firefox%2C%20Portable%20Ed./Mozilla%20Firefox%2C%20Portable%20Edition%209.0.1/ The English versions are at bottom of links list.