Except where noted, everything here applies to both Firefox 121 and the Firefox 115.6 ESR.

Other Changes

• In some situations, Firefox now offers to set itself as a mailto handler when you visit web based email. If you want to disable this behavior, you can set the preference browser.mailto.prompt.os to false. For more information, see bug 1864216. (This only applies to Firefox 121.)

Policies

• The Preferences policy has been updated to allow disabling the certificate and devices dialogs using the preferences security.disable_button.openCertManager and security.disable_button.openDeviceManager. They must be locked to function correctly.