Hey, You can press CTRL+SHIFT+A, it will open the extensions page. From there you can disable the add ons you don't want.

Mon Firefox est installé sur un Mac et CTRL+SHIFT+A n'a aucun effet merci

In Mac CTRL is replaced by Command. You can try that or a direct way to access add ons is Click the menu button (on the top right)Menu and choose Add-ons. The Add-ons Manager tab will open. Select the panel for the type of add-on you wish to view or manage, such as the Extensions or Themes panel. Check this link for better understanding. https://support.mozilla.org/en-US/kb/find-and-install-add-ons-add-features-to-firefox