I have faced a strange problem when trying to install Adobe Flash Player for Mozilla Firefox (version 56) using the online installer. When you visit the official Adobe Flash download page, the Adobe server automatically identifies your browser and OS version, and its bitness. In my case, it correctly identified that I was using Windows 10 x64 and Firefox browser. So I was suggested Flash Player distribution for my environment.
During the installation of the downloaded Flash Player (flashplayer26_ha_install.exe) installer file, the following error appeared:
Application initialization error
After I clicked Finish, the downloaded file flashplayer26_ha_install was automatically deleted.
Having opened Flash Player installation log, Adobe_ADM.log (located in C:\Users\Username\AppData\Local\Temp\Adobe_ADMLogs), I found some strange errors of connection to Adobe servers and a certificate error.
11/18/17 11:31:10:788 | [WARN] | | ADM | | ApplicationContext | HTTPSend | | 7792 | Certificate not matching.
11/18/17 11:31:10:788 | [FATAL] | | ADM | | WorkflowManager | HTTPConnectorError | | 7792 | Error occurred while getting application xml: -4 extended error: 0
It felt like the installer could not connect to Adobe servers to get files. In this case, the solution was to download and install the full (offline) version of Flash Player distribution. However, it was very hard to find it on the official website. Having spent a long time searching, I managed to find the page to download offline installers of Adobe Flash for Windows: https://helpx.adobe.com/flash-player/kb/installation-problems-flash-player-windows.html
After that, Flash Player was installed without any problems.