For more information, see the articles Set Adobe Flash to "click to play" on Firefox and Why do I have to click to activate plugins?
If you want Flash to work in Firefox you must install the plugin version, as explained above.
If you see an "Activate Adobe Flash" prompt instead of Flash content, either you have set the Flash plugin to "Ask to Activate" in the Add-ons manager or Firefox has prevented an unsafe Flash version from running automatically.
Click on the "Activate Adobe Flash" message to allow the Flash content to load (if it doesn't, reload the page and try again).
The Flash plugin automatically updates itself by default.
If Mozilla's Plugin Check page or Adobe's test page says that Flash is outdated and you don't want to wait for the automatic update, you can update Flash manually by downloading and installing the latest version from Adobe.
To check if your installation of Flash is up to date, visit Mozilla's Plugin Check page.If it says that Flash is outdated, you can update Flash by downloading and installing the latest version from Adobe.The Adobe Flash Player browser plugin lets you view video and animated content in Firefox.This article has information about testing, installing, updating, uninstalling and troubleshooting the Adobe Flash plugin.Note: The Firefox Software Update feature does not update installed plugins.See the Adobe Security bulletins and advisories page for information about security and stability issues affecting Adobe Flash Player and other Adobe products.