can't add video downloader extension

[sandhill]

When I can even find "more tools" it does not have the addons option.

[DavidR]

Well the purpose of a Secure browser is not too all all and sundry Add-ons to be added, so there will be a limited range of approved add-ons.

If you us it only for secure tasks that shouldn't be an issue, but by all accounts it does allow some.  I don't use ASB so I can't speak from personal  experience..

I suggest you read this FAQ - https://support.avast.com/en-us/article/29/#pc
Particularly scroll down to - What is Extension Guard? - and - Why does Avast Secure Browser block some downloads?

Hopefully that will give you an idea.