See if this matches your issue. https://blog.mozilla.org/security/2012/10/11/click-to-play-plugins-blocklist-style/ Please come back and mark this as solved if this works or please provide more info to see if can help further as ver 48 was the cut off for changes and think it was ver 10 something of Flash

The whole idea of the change is not running XP as it is out dated and Flash is a security risk especially older versions like you are using. Linux looks ok unless need XP for a program.

I do not recommend it but link to version 47.02 download and save full installer https://ftp.mozilla.org/pub/firefox/releases/47.0.2/ then google how to stop FF from updating and save info for of line viewing and disconnect from internet and install ver 47 then apply the stop updating info.

Again though this is not recommended.

Any use of this information is at your own risk