Your Firefox reported that it is running on Windows 7. If that is true, then there won't be a Firefox update to make Amazon happy. As a test, could you try setting the following value to see whether it fools Amazon:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported.

(2) In the search box in the page, type or paste forceVersion and pause while the list is filtered

(3) Double-click the network.http.useragent.forceVersion preference to display an editing field, and change the value to 128 then press Enter or click the blue check mark button to save the change.

If you try Prime Video again in a new tab, does it still give you the same message, or does something else happen now?

In case the problem is not your Firefox version but your Widevine version -- that's the plugin for digital rights protected media -- could you check your current version on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Plugins. On the right side, click "Widevine Content Decryption Module provided by Google Inc." to open its Details panel. What version do you have?

Thanks for prompt reply. Need time to process your info, bit complicated for me! Had no problems few days ago.