Also remember to uninstall all older versions of Java before updating to the latest.
Firefox has determined that the following add-ons are known to cause stability or security problems."
And then it recommended and gave me the option to disable it.
Does that sound strange?
No, it doesn't sound strange to me as that is the developers of Firefox at Mozilla looking out for your security. Java is much like Windows; vulnerabilities are discovered that need to be patched with an update. No one knew the vulnerability existed when Java was installed, but, once discovered, and once Mozilla has been informed, they have in turn informed you that the Add-On (in this case a plugin--Add-ons are both plugins and extensions; check the tabs in your Add-On Manager) is unsafe. If it's a newly discovered vulnerability, I recommend that you take Mozilla's advice and disable the Add-on until a patch is issued. For Java check their website for the latest version. In your case, you already had an old version of Java installed when you installed Firefox, so the Plugin being unsafe had been known for some time and updating to the latest version will fix the problem, as RedDawn
And.....aren't Firefox add-ons usually OK and not known to cause problems?
Actually, no, just the opposite. When having problems with Firefox, usually extensions are the first things looked at when troubleshooting. That is why Firefox has a safe mode, which can run it with all Add-Ons disabled.http://support.mozilla.com/en-US/kb/Safe+mode
I think your question may actually be more along the lines of "Isn't Firefox supposed to be a safe browser?" And the answer is that Firefox is safer
than other browsers, but not absolutely safe as there is no such thing for any application in Windows. Firefox is no magic bullet. They do a pretty good job of patching holes in the browser when discovered, but Add-Ons and especially extensions, are higher risk as they are controlled by third parties and there are way too many of them for Mozilla to vet every one. That being said, Mozilla also can be questioned on some of its security policies. For example, up until a few versions ago, it allowed some extensions to be hidden from the Add-ons manager and there are still some extensions that take a registry edit to uninstall.
So keep an eye on your own security--don't trust a browser to do it all.