Can one of your could try to watch something at that url to see if you receive this error ?
I think I was able to watch from Elive but I am not sure…
A later version of Mozilla Firefox is required for Prime Video. To update, click the menu button (three horizontal stripes) on the web browser toolbar, click About Firefox , and then click Restart to update Firefox .
Please note that GNU/Linux distributors may provide packages for your distribution which have different requirements.
Firefox will not run at all without the following libraries or packages:
GTK+ 3.4 or higher
GLib 2.22 or higher
Pango 1.14 or higher
X.Org 1.0 or higher (1.7 or higher is recommended)
libstdc++ 4.6.1 or higher
For optimal functionality, we recommend the following libraries or packages:
NetworkManager 0.7 or higher
DBus 1.0 or higher
GNOME 2.16 or higher
PulseAudio
I Installed Chrome in my Ubuntu VM, so if I need a more recent browser for some very serious and specific task ( like watching something on Amazon movie lOL) I will use my VM