After trying for days to get chrome/Internet Explorer/firefox to allow java applets, I just could not get any of these browsers to work. Here is what I did instead -
Download the Pale Moon browser here. It is an open-source browser for windows and linux that still supports NPAPI plugins (java). I would recommend only using this browser for p4. Modern browsers do not support NPAPI or java plugin anymore because of security issues.
Then go to java.com and download the latest version of java. Pale moon would not load p4 until I downloaded and installed the latest update for java.
Hope this helps.
Edit - Here are some additional steps I needed to take in order to get p4 running on my windows 10 laptop-
Add "phantasia4.net" and "phantasia4.net/cgi-bin/p4_client.cgi" to java exception site list. (google search "configure java" if you don't know how to do this)
Open Pale Moon Browser, press ALT to see menu bar > tools > options> content> uncheck the "block all popups box".
Open Pale Moon Browser, press ALT to see menu bar > tools > options> security> change the "add-on security level" dropdown to off. (setting this to off is dangerous, only use this browser to play p4).
Then close and reopen pale moon as administrator. Happy holidays!