Hi

When Mozilla becomes aware of add-ons, plugins, or other third-party software that seriously compromises Firefox security, stability, or performance and meets certain criteria, the software may be blocked from general use. For more information, please read this support article.

Security flaws have been identified in Flash that could lead to users inadvertently downloading "ransom-ware" (for example; Cryptlocker) through users visiting a site that has toxic code embedded in it. Adobe has recently published an updated version that (should you need Flash) I recommend you download.

It is up to you whether you wish to continue to use Adobe Flash. There has been a number is security related issues with Flash recently and whilst Adobe have released updates, you may wish to reevaluate whether you want to keep updating Flash for the video content you look at.

You should be able to watch Youtube videos using Firefox without Flash. Youtube makes its videos available over HTML5, which Firefox can view without any additional software. I do not have the Adobe Flash plugin installed myself and I can view Youtube videos without a problem.

I hope this is of assistance, but if not, please come back here and we will see what we can do to help.

Mozilla had "soft-blocked" version 18.0.0.203 and earlier, which still allowed you to activate Flash on sites you trust.

Adobe did release new updates today for Windows and Mac OSX (yet to for Linux). https://www.adobe.com/products/flashplayer/distribution3.html

On WinXP you might want to consider using the Extended Support Release - Flash Player 13.0.0.305. The newer versions of Flash provide features that WinXP can't use - features only available in Vista and newer Windows OS's.

Scroll about 3/4 of the way down this page. https://www.adobe.com/products/flashplayer/distribution3.html

Grab the WIndows > Plugin-based browsers --> EXE installer version.

But before installing it, you should first run the Adobe Flash Uninstaller to get a clean installation of Flash. http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html