If you open a file since Adobe Acrobat, the Recent Documents is not updated.
If you open a file since Adobe Acrobat in MS Windows, the Recent Document IS updated.
When you download a file since Firefox, the Recent Documents is not updated.
When you download a file since Firefox in MS Windows, the Recent Documents IS updated.
I think the problem is in the system Gnome and not in each application.
Other programs and systems:
If you open a file since Adobe Acrobat, the Recent Documents is not updated.
If you open a file since Adobe Acrobat in MS Windows, the Recent Document IS updated.
When you download a file since Firefox, the Recent Documents is not updated.
When you download a file since Firefox in MS Windows, the Recent Documents IS updated.
I think the problem is in the system Gnome and not in each application.