I am running Windows XP and Firefox 38.0.5. I successfully downloaded, saved and opened the installation file. However, an attempt to run the installation file failed. The message returned: "Installation failed. Click "Finish" for further assistance." I referred to the Adobe help pages and checked the Firefox plug-in page, which told me the Flash Player version that was installed and provided a link to update. That link took me back to the start of the installation process, which failed again in the same way. I then uninstalled the existing Flash Player version, rebooted the computer and tried again with identical results. I then went to the Firefox "Check Your Plugins" page which says an old version is installed. The message is: "Adobe Flash Player RealNetworks(tm) RealDownloader PepperFlashVideoShim Plug-In outdated 188.8.131.52". This version does not appear on the Windows Control Panel Add or Remove Programs list, so can't be uninstalled.
Can you please clean up your machine using our uninstaller, Please find the instructions and uninstaller at location - Uninstall Flash Player | Windows. Once complete with uninstaller use our offline installer for mozilla, you can find the installer at location - Installation problems | Flash Player | Windows
Please let me know if this helps.
Thanks. I temporarily disabled my antivirus program and successfully installed Flash Player.