Enter about:config into your Firefox address bar Click the I'll be careful button Find xpinstall.signatures.required in the list Right click the preference Select Toggle until the value is false

Security Issue: Update your Flash Player Version 20.0.0.267
https://www.adobe.com/products/flashplayer/distribution3.html Note: Windows users should download the ‘’’active_x’’’ for “Internet Explorer,” and the ‘’’plugin’’’ for “Plugin-based browsers” (like Firefox).

Note: Windows 8 and Windows 10 have built in flash players and Adobe will cause a conflict.

See if there are updates for your graphics drivers https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

https://support.mozilla.org/en-US/kb/update-firefox-latest-version 43.*

Current Firefox releases require extensions to be signed to prevent abuse by malware. In Firefox 43 unsigned extensions will be disabled by default. Firefox 38 shouldn't be affected normally.

You can set xpinstall.signatures.required to false to disable this security feature in Firefox 43. In release and beta builds of Firefox 44 and later you can no longer override this.

See:

• http://www.ghacks.net/2015/12/16/what-you-do-when-firefox-disables-installed-add-ons/