What's their computer system and Firefox version? Please explain the problem in detail. What happens? Error messages?

It is a major Security update in code and has a Sandbox that important files run in. The W3C.org (World Wide Web Consortium) in charge of standards and practices and future makes the rules and Mozilla abides by them. Thus major update. How about looking at these 2 URL's first : https://www.howtogeek.com/333110/how-to-customize-firefox-quantum-and-remove-the-white-space-around-the-title-bar/ and The name is not descriptive enough : https://www.howtogeek.com/332449/whats-new-in-firefox-quantum/ More information will come out slowly. New extensions are being made and some older ones being updated that can track here : http://bit.ly/2j0Anlj Going back : unfortunately 56.0.2 is no longer safe to use for every day use, but 52.5.0 ESR is! It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ Note : Legacy Extensions will be deleted or removed in any version update after May 2018. You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore- Is there something specific we can help you with and or what is missing from the older versions that you can not find in this one. Please let us know if this solved your issue or if need further assistance.