mailto

I use Linux Mint with Mozilla Thunderbird for an e-mail client. When it use this extension, it pops up a window to allow it to "Open xdg-open". The pop-up has a pick to allow the extension to "Always allow", which would be great if the pick worked. The pop-up asks for permission every time I use it, even if I click the "Always allow" box. It does work if I allow it to use xdg-open each time.