I think Firefox would normally open to your default Downloads folder. You can check on that setting on the Settings page:https://support.mozilla.org/en-US/kb/where-find-and-manage-downloaded-files-firefox#w_change-where-downloads-are-saved

If you notice this across your applications, that they want to save videos or other types of content in OneDrive instead of your Documents or Downloads folder, there is a system setting for that. In Googling around, it could be this one:

• In the Windows 11 search box, type or paste storage settings and click the main result, which should open the Storage Settings control panel
• Scroll down and click on "Advanced storage settings" to list specific categories
• Click "Where new content is saved"
• If there is a category which points to OneDrive, change it to your C drive (or if you prefer a different local drive, that drive)

I really appreciate your efforts to solve my problem, and I tried your suggestions, but I still have the same problem.

I just re-read your original question and you mentioned your virtual desktop. Is that something different than the user profile desktop at

• %userProfile%\desktop
• C:\Users\<username>\Desktop

I only used that term to indicate the "desktop" on the C drive, as opposed to the mechanical desktop computer. Again, thank you for trying to help.

I doubt you can just download Youtube videos from the Browser or any other Browser. Google implicit protection to prevent video thefts. You have to use 3rd party bypass that isn't Addon to even do what your asking. I found this from experiences in Youtube Videos.