I've using a Windows 7 laptop for Firefox 50 and updated Firefox, then uninstalled them and reinstalled them but the add-on extensions area still shows that there are 3 versions of Shockwave Flash (20, 21 and 22) but the animation will not work. After uninstalling Flashplayer they did all leave but after installing just one file all 3 returned. All 3 are asking to be updated and they just go to the regular update page with the 2 extra items that I always deselect. Also none of the versions shown have an "Always activate" option because they are all greyed out. The only options available is the "Ask to activate".
Firefox says the following but when you try to use their Update page the Download Manager is just blank. So when I do update I go to the Installation problems | Flash Player | Windows 7 and earlier page and select the Firefox option "Flash Player for Firefox - NPAPI" in "Still Having Problems?" part
When the about:addons page is showing multiple versions of Flash it usually means there's a Flash Player file somewhere on the system that the uninstaller isn't removing. Please perform a clean uninstall (See How do I do a clean install of Flash Player - Windows?) but perform the following steps after step 7
At this point you should only have one version of Flash Player installed.