Check IF (you have the Avast video downloader installed by using the Diagnostic information)
{
1- Press F10 and then Enter (NOT at same time, but in that order).
2- Click on settings (a context menu will open at the right of your browser with different options, click on Settings.
3- Go to the last option on left tab which should be "About Avast Secure Browser" it's green.
4- Click on Diagnostic Information.
}
In there you will find all your extension list, and also the Enabled and Disabled Extensions.
IF {you find the Avast Video Downloader Disabled in there},
THEN
{
1- Just go to secure://extensions/
2- click on Developer mode switch button (green is on, grey is off) obviously.
3- look for Avast Video Downloader and turn on the extension.
}