Staden

This is a security measure Librewolf has. You can fix this in the settings.
Edit: Follow these steps to fix it

• Click on the padlock button on the URL bar at the page where you want to upload your image
• Click on "Connection secure" or whatever is written on the bar with another padlock icon
• More information > Permissions > uncheck "Extract canvas data" and select "Allow"

This will affect the current page only