About the error
Antivirus and other security software can sometimes prevent the Lean Library extension from being installed or updated automatically in Firefox. If this happens, please follow the steps described below in order to successfully install our extension.
What to do
1: Open a different browser, like Chrome, Microsoft Edge or Opera
2: Copy and paste the link below into your browser to download the Lean Library extension. It will be saved as a .xpi file in your Downloads folder.
https://addon.leanlibrary.com/firefox/latest.xpi
3: Go to your extension settings in Firefox by visiting about:addons
4: Drag-and-drop the extension installer file among your other extensions
5: The extension will install