I once had the same problem. A program had gotten into my computer, and shut down my anti-virus. I had a lot of fun trying to stop it ( NOT ! ). Once I found the program, I sent it to the anti-virus people, and a few days later the program was updated.

BTW, this is the page the user was talking about.

https://support.mozilla.org/en-US/kb/how-does-phishing-and-malware-protection-work {web link} How does built-in Phishing and Malware Protection work?

It's more likely this setting was carried over from an earlier version of Firefox. Some people disable one type of protection in favor of the other. Or disable the malware & phishing protection when troubleshooting other issues. Like to reach sites that Google says are bad but really are false positives.

You may have forgotten fooling with that setting or unchecked it by accident. For example, go back to the Security section in the Options. Move your mouse all the way over to the right underneath the "Exceptions" button and click your mouse along that area for each setting. You see how easily they could be changed by a misclick?

But since you say this happened on 2 computers, I'll ask a few people to test this out and see what happens.

You also said you had a anti-phishing incident? Could you elaborate a little more on that. I'm guessing you were in your email and opened a email you thought to be legitimate?

You'd only have been safe in that case if Google's database had been updated with info to block that exact phishing attack. Did you try revisiting the actual phishing attack after activating the protection? I'm curious to know if it was blocked.

Hi

Thanks to all for the assistance. I have the anti-phishing on now and it seems to be working. Perhaps the setting was carried over from an early version of Firefox, also possible some other software interfered with proper installation. Unfortunately I can't retest it. Perhaps my terminology of phishing was incorrect; what happened was that a notification appeared on screen (on the Windows 8.1 PC) while reading a news article thru Google News. It looked like an official Microsoft/ Flash Player update notification telling me an urgent security update needed to be installed; it was really from a company impersonating Adobe. I aborted the download and checked the official Adobe site; I already had the latest version – I reported the company to Adobe. My bad for breaking my rule of never clicking “yes” on a pop-up message while browsing the web.

That's not really phishing, that sounds like malware rather. Try running some scans. Troubleshoot Firefox issues caused by malware