Firefox v52+ disables all plugins except for Flash Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work? {web link}

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

Note: You can have more than one Firefox version on the computer.

How would I go about creating multiple versions of Firefox on the computer? We need FFX 55.0 for my wife's schooling programs, but I need a version that runs the Java websites. It would solve things if I could have two shortcuts, one for each version. I understand the security risks, the older version would just be to run those specific Java programs.

When you run the installer, switch to Manual and select a folder name to place the program into. Note: you should also create a user profile for that program since there are settings and add-ons that don't work properly.

Note: the last Firefox program install will be listed as the default web browser. Open each Firefox and turn off the option to check that this is the default browser when the browser opens. The browser you want to be the default, leave the option on.

Here is an example of how to create a shortcut to open the Firefox you want and its profile.

C:\PROGRA~2\MOZILL~4\firefox.exe -P FirefoxESR -no-remote -new-instance -new-window http://comicskingdom.com/conceptis-kakuro/today +++++++++++++++++++++++++++++++++++++++++++++++ Usage: C:\PROGRA~1\MOZILL~1\firefox.exe [ options ... ] [URL]

      where options include:

 -h or -help        Print this message.
 -v or -version     Print Firefox version.
 -P <profile>       Start with <profile>.
 -migration         Start with migration wizard.
 -ProfileManager    Start with ProfileManager.
 -no-remote         Do not accept or send remote commands; implies -new-instance.
 -new-instance      Open new instance, not a new window in running instance.
 -UILocale <locale> Start with <locale> resources as UI Locale.
 -safe-mode         Disables extensions and themes for this session.
 -console           Start Firefox with a debugging console.
 -jsconsole         Open the Error console.
 -browser           Open a browser window.
 -new-window  <url> Open <url> in a new window.
 -new-tab     <url> Open <url> in a new tab.
 -preferences       Open Options dialog.
 -search     <term> Search <term> with your default search engine.
 -setDefaultBrowser Set this app as the default browser.

For Windows, another option is to use the PortableApps version of Firefox 52 ESR. This installs into a folder completely separate from your normal Firefox profile so you don't have to worry about file compatibility issues between Firefox 55 and Firefox 52.

More info: https://portableapps.com/apps/internet/firefox-portable-esr