I'm having the same issue as the OP. I try to install Flash Player 126.96.36.199, and the installation gets to 50% and then gives a "Installation failed. Click finish for further...". So I decided to look for a separate download for Firefox. It keeps promting for Admin Rights even though I'm the admin. This is so frustrating.
You're issue is not the same as the OP. The Admin privileges pop-up error issue being reported only affects the ActiveX Control. Since you're issue is with the NPAPI (Firefox) plugin it's not the same issue. Please start a new topic for your issue and provide the following information:
- Operating system version
- Web browser and version
- Flash Player version
- Explain your problem in step-by-step detail if possible
- If you get error messages, please provide a screenshot
Please see Re: Admin Privileges Error Popup Adobe Flash 188.8.131.52 with admin credentials for updates on the Admin privileges issue. Please note that the pop-up error is erroneous as Flash Player ActiveX is updated.
Locking this topic.