Quote:Mozilla plans to introduce a change in upcoming versions of the Firefox web browser that blocks extensions from running in private browsing mode by default.

Firefox makes no distinction between regular and private browsing mode in regards to browser extensions currently.

Opera browser, another Chromium-based browser, disallows extensions as well but supports options to allow them in the mode explicitly. The same functionality is provided by Microsoft Edge.

Another core difference between Firefox and Chrome in private windows is that Chrome users cannot restore closed tabs in that mode.

Mozilla plans to implement changes that follows Opera Software's and Microsoft's implementation: extensions are disallowed to run in private browsing mode by default but users get options to turn them on explicitly in that mode.

The feature is hidden behind a preference currently and only available in Firefox Nightly builds. It is not clear yet when it will land in Firefox Stable.

Full reading: https://www.ghacks.net/2019/02/01/firefox-will-soon-disallow-extensions-in-private-mode-by-default/