Flash Player uninstaller will not remove any integrated/embedded version of Flash Player. It will only uninstall user-installed Flash Player versions.
For Edge you can try uninstalling the Flash Player for IE/Edge Windows Updates, which may or may not work. Uninstalling updates is very time consuming and requires system restarts for each update that is uninstalled.
For Chrome:
Chrome will always launch the most recent version of Flash Player on the system. If you install a previous version and the integrated version is more current, then Chrome will use the integrated version. To get around this, rename the folder the integrated version of Flash Player is saved in and Chrome will use the manually installed previous version.
The integrated version is saved at C:\Users\<YourUsedID>\AppData\Local\Google\Chrome\User Data\PepperFlash\<FlashPlayerVersion>. Navigate to C:\Users\<YourUserID>\AppData\Local\Google\Chrome\User Data\PepperFlash and rename the Flash Player version folder (e.g. rename 28.0.0.126 to something like backup_28.0.0.126). Install the version you wish to test with and Chrome will load that version.
Note that Chrome blocks Flash by default, forcing users to enable it for each site visiting. In addition, since you'll now be using an older version of Flash it'll display an additional warning. For example, after doing the above, I:
- Navigated to https://helpx.adobe.com/flash-player.html
- Clicked the 'Check Now' button. Flash was still disabled.
- Click the Info icon to the left of the address field and selected 'Site Settings'
- In the new tab, for the Flash setting, I selected 'Allow'
- Went back to the original page (https://helpx.adobe.com/flash-player.html) and reloaded the page (Chrome will prompt you to reload the page after changing the Flash Player settings)
- Chrome detected I was attempting to use an older version of Flash and displayed the following warning

- I clicked 'Run this time' and Flash content displayed.
The above ONLY runs Flash for that time. If you navigate to a different page, reload the page, Chrome will block Flash again and you'll need to run it again for that site - essentially you'll be prompted to run Flash for every page that has Flash.
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When finished go back to the C:\Users\<YourUsedID>\AppData\Local\Google\Chrome\User Data\PepperFlash\ folder and rename the Flash Player folder back to just the version number.