If the FF automatic updates were enabled, then FF V57 will install itself after the next time you close FF, or restart the computer. You will have to let that happen, and then follow the procedure below. .
I am working under Windows 7. The details may vary slightly under other operating systems.
Select the version that corresponds to your preferred language, download it and save it to a convenient place. The en-US\ directory has the US English version.
Then close Firefox.
Working under Windows 7:
Go to Start menu -> Control panel -> Programs and Features
Uninstall Mozilla Maintenance Service if present.
Uninstall Mozilla Firefox version 57
Close control panel.
Run installation of Firefox 56.0.2 installation program that you downloaded.
During installation, uncheck the box that says: Install Maintenance Service?
If FF was installed to a non-default location, select the custom install option and direct the FF installer to the desired directory, else the standard install is OK.
Allow FF to start.
Open the FF Tools-> Options -> General menu, scroll down near bottom and check the “Never check for updates (not recommended)” option.
Then open the FF Tools-> Extensions menu. If Greasemonkey 4.0 has been installed, then select the “Remove” option and remove it.
When completed, Type “Greasemonkey” in the “Get Addons” search field at the top of the page. FF should find the old Greasemonkey 3.17 version. Install it and restart FF.
When FF comes back, the Tool -> Addons menu should show a new Greasemonkey entry in the left column. Select it, and the two Allscripts scripts should still be there, though then have been deactivated on some of my computers. Reactivate any that have been deactivated, and you should be back to normal operation. You will have to download then again from the GreasyFork repository if they have disappeared.