Allow me to disagree and to tell you what happened last weekend:
Last Sunday I had a call from my stepfather who "couldn't run the website to order agro food" anymore. This website runs a Java applet to manage agro food orders on-line and the code isn't signed (it's a small structure).
He tried to understand what was going on with the warning before clicking "ok/yes/run". He googled the warning and unfortunately ended up installing malwares from ads running on some PC help website/forums that promised to fix "2 just found vulnerabilities": he thought that was related since the warning actually preventing him from accessing his "working-fine-yesterday" website seemed to be about security and vulnerabilities in the plug-in.
He then tried to update Java but canceled it at the end of the process because the window with the Java propaganda ("it powers 3 billions of applications, your car, your website, etc.") looked too much like the one with malwares from before and those didn't fix the problem (not being able to access his website).
When I finally could go to his house to fix it I realized what had happened.
It is definitely not user-friendly. It was working before and in his eyes Mozilla made it not working anymore.
edit: typo and grammar