Hi, Private Browsing has no effect on add-ons - Private Browsing - Use Firefox without saving history. You can still disable any add-ons manually by going to the 3-bar menu > Add-ons > Extensions/Plugins, but this won't be changed by whether you are in normal or private mode.

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PB mode only means that no session data is stored to the Firefox profile folder. In all other ways PB mode works the same as regular mode and that includes extensions. Some extensions may behave differently in PB mode like for instance Firefox screenshots that only allows to download (store) the screenshot locally. Other extensions may also have restrictions in PB mode, you would have to check the extension's page(s) for such restrictions.