So, we recently released the new AVD 3.0 for the new browser Mozilla Firefox 57.
After that we begin receiving comments from users, and often there are complains that AVD works differently, or requires something else to install, or does not download something, etc.
The first thing that should be stated is: Firefox is different now. And thus AVD is different extension now as well. It is built using new technology and has nothing in common with the old AVD.
For now, it has not all features that previous AVD had, but we will bring everything back with time.
The second thing is that previous Firefox had been providing a lot of possibilities to extension by means of XPCOM API. Extensions could launch external applications, read, create and write files on disk. Add-ons built with WebExtensions technology have limited power. They are running in strictly sandboxed mode.
Previous AVD could directly call video converter ffmpeg to process downloaded video segments into a single video file. The new AVD cannot directly call external programs, because simply there is no such WebExtensions API available.
On the other hand WebExtensions-based add-on can ask web browser to communicate with some external program. Such external program should be specially designed for that purpose.
That's why we introduced new component of AVD called native messaging host application, or simply native application.
For the sake of security, WebExtension add-ons cannot install any additional software. There is no such API and will never be. You have to explicitly download and install native application.
Native application that we created has low level privileges, it is installed only locally into AppData\Roaming folder of your account. It does not have access to system files, machine-wide registry hives, other users' files, etc. So you can be sure about it.
Video converter ffmpeg that was used by previous version of AVD existed long before AVD ever appeared. Volunteer developers all over the globe managed to create versions of ffmpeg for Windows, Linux, Mac OS X and other operating systems. That's why you could use AVD for Firefox on Windows, Linux and Mac OS X.
We will also need to create native application for Linux and Mac OS X, because there are a lot of users of AVD who use those operating systems. And thus will be.
We hope that some things made clear for now.
Check https://www.ant.com/video-downloader for new versions and do not hesitate for contact support.ant.com for additional questions.