Get the full installer from https://www.adobe.com/products/flashplayer/distribution3.html

It's possible that is a malware come-on, since your Question Details > More System Details shows Shockwave Flash version 19, which is the current version.

I suggest using some of the free scanning/cleaning tools in our support article: if they want money to clean, you have a serious infection and you should try the specialized forums listed in the article: Troubleshoot Firefox issues caused by malware.

I also suggest the following for tracking down and cleaning up bad add-ons, hijackers, and ad injectors.

(1) Open the Windows Control Panel, Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help surface undisclosed bundle items that snuck in with some software you agreed to install. Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it. Take out as much trash as possible here.

(2) Open Firefox's Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons
• in the Windows "Run" dialog, type or paste
  firefox.exe "about:addons"

In the left column, click Plugins. Set nonessential and unrecognized plugins to "Never Activate".

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. Bear in mind that all extensions are optional, none come with Firefox, and you can learn more about them by checking their reviews on the Add-ons site.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?