"Download failed. Please check your connection." When attempting to install extensions, June 4, 2019.
Who remembers this error from before (about this time last month)? Yeah, I don't know if others are having this problem, but I sure am. Only 2/8 of my extensions reinstalled after moving over to Firefox on Linux (sync is enabled), and attempting to reinstall them results in the "Download failed. Please check your connection." error. As with other posts near May, I am connected to the internet, and I even tried a VPN that I luckily was able to download but to no avail.
Hi TodayIsADay, your Firefox identified itself as version 66.0.3. That version did not have the updated certificate needed to verify older extension signatures. Are you limited to that version or can you update?
Try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.
Note that current is Firefox 67.0.1.