|Dec. 11, 2016, 2:33 p.m.|
I've tried uninstalling and reinstalling the add-ons, but it doesn't help.
On my previous computer, the ""Video DownloadHelper" add disappeared too, so I was excited that it worked with the new computer. When it had disappeared on my old computer, I couldn't figure out why. However, now it seems to have coincided with installing "Toolbar Buttons".
Perhaps it is a coincidence, but it definitely seems like Toolbar Buttons made my "Video DownloadHelper" disappear.