The add-on could not be downloaded because of a connection failure
1] Manually Download Extension
Just before we start, since we are downloading a file, I will suggest using a download manager. In case of issues, you can resume the download. 2] Enable xpinstall flag
While these two should be enough to download the extension in case of a connection failure, sometimes you need to wait. It could be a temporary issue that gets resolved on its own. In the end, I will recommend using VPN software. If there is anything that your ISP is blocking, the VPN connection should be able to resolve. I hope you were able to fix the issue, and get rid of the error message—The add-on could not be downloaded because of a connection failure – Firefox error.
