Keep using Flash Player in browsers in 2021

It’s 2021 now, and Adobe Flash Player has been end-of-life after December 31, 2020. There are many cases where you want to retain it, however. For example, you may want to keep enjoying an old game that’s been around for decades, or managing your organization’s infrastructure via VMware vSphere Flash Web Client (vSphere 6.5 and older).

Quick Solution

According to Adobe Flash Player 32.0 Administration Guide, page 28 and 36, you can deploy a config file named mms.cfg with the following content to continue using Flash on whitelisted sites:

EOLUninstallDisable=1
SilentAutoUpdateEnable=0
AutoUpdateDisable=1
EnableAllowList=1
AllowListUrlPattern=*://*.example.com/
AllowListUrlPattern=*://*.example.net/
AllowListUrlPattern=*://*.example.org/
AllowListUrlPattern=file:*

TraceOutputEcho=1

Depending on your operating system, the file may be located at:

• Windows: C:\Windows\System32\Macromed\Flash and C:\Windows\SysWOW64\Macromed\Flash (if you’re on a 64-bit Windows)
• macOS: /Library/Application Support/Macromedia
• Linux: /etc/adobe (yes it is Adobe instead of Macromedia)

Placing the mms.cfg file inside the correct directory (both directories for 64-bit Windows) should enable Flash on websites you whitelisted.

Additionally, if you’re using Google Chrome or Chromium-based Microsoft Edge, you need to place an additional mms.cfg file in the following directory:

• Windows: C:\Users\<username>\AppData\Local\Google\Chrome\User Data\Default\Pepper Data\Shockwave Flash\System\mms.cfg
• macOS: /Users/<username>/Library/Application Support/Google/Chrome/Default/Pepper Data/Shockwave Flash/System
• Linux: ~/.config/google-chrome/Default/Pepper Data/Shockwave Flash/System/

For Microsoft Edge, replace Google with Microsoft and Chrome with Edge in the above paths. Don’t forget to replace <username> with your user name.

After placing the mms.cfg file, just restart your browser to see Flash come back again.

The Future

The Chromium browser (basis of Google Chrome and modern Microsoft Edge) will completely remove Flash since version 88, and so will Firefox since version 85. This means you can no longer enable Flash even with the above Enterprise policy applied.

Unfortunately, you have to keep an old version of your browser of choice around if you plan to use Flash for an extended period. This means you have to find an available download, and disable the auto-update feature for the browser. You will be missing the latest web features and security improvements if you remain on an old browser, which will be an issue sooner or later.

You can get around the browser issue by using Internet Explorer if you’re on Windows, which is already lacking new web features and security. You’ll want to prevent Windows Update KB4577586 from installing, following Microsoft’s guidelines.

A better approach is to keep the Flash Player installers around (I saved FP v29 here if you need - it’s a full set so beware of download size - 421 MB), and install them when needed.

Finally, the only way to secure your ability to use Flash in the distant future is to install a virtual machine running an older system (like Windows 7), with old software and old browsers, and then put your Flash Player there.