You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for a good ad / pop-up blocker.

Thanks to FredMcD for the suggestions.

Problem isn't solved, and here is what I've done: - Reinstalled from a recent backup; I had made the backup before the problem started manifesting itself, but it seems the root cause was already present. - I ran my virus scanner, Bit Defender free version, which didn't find anything. - I ran Bit Defender's Adware Removal Tool, which didn't find anything. - I purchased and ran Adware Doctor; it identified a plist file, which I trashed. - I reviewed Mozilla add-ons but decided against general ad blockers because I want to find and kill the root cause, not just cover up the ads shown; but I did add Privacy Badger.

Recall that when I'm logged in to Yahoo mail, the page spontaneously goes to spam sites. Before I took all these actions it was one of three sites, not it is only one but perhaps my time sample is small.

Also, I logged out of Yahoo mail, staying at the Yahoo home page, and it stays on the page.

Finally, I logged in to Yahoo mail from Safari, and the problem occurred there also. So this isn't a Firefox problem. But it is interesting that I see the problem only when logged in to Yahoo mail.

Thank you for any other advice you can offer.

Well done, You should contact Yahoo support and complain.

An ad blocker should help.

Thanks again, Fred.

I filed a support request with Yahoo support.

Good advice on the ad blocker, though in this case I want to find the root cause before I remove a symptom (as annoying as it is). It is possible the malware is doing something bad I can't see.

Yahoo support will not be able to do anything to you. Generally, once malware is in, you are going to have a bad time. Yahoo is a spam ridden platform that shouldn't be used by anyone, unfortunately, the reality is different. I know some of the steps you tried, but I would like you to repeat them in a thorough manner, the following steps should clean it up:

1. Restart your PC in “Safe mode with networking.” 2. Install and run RKill to kill malicious processes and services 3. Check your Programs and features and see if there are any new recently installed programs that you don’t recognize. If there are, remove them. 4. Check your add-ons once more, if you find anything suspicious, remove it. 5. Use browser specific cleanup tools and uninstall all of the browsers. 6. Check your task manager for any suspicious processes, if found, identify folders and try to remove them manually. Or just "Win key + R" and type %appdata%. Afterward, delete potentially malicious folders. 7. Do a full scan with anti-virus software of your choice or use Windows Defender (offline) to clean up initial infections. 8. Scan your PC with Hitman Pro, Malwarebytes, and AdwCleaner. Multiple anti-malware solutions will confirm that the threat was removed. 9. Clean up your Registry and Cached files with CCleaner 10. Restart your PC in normal mode and do an additional scan to confirm that the malware is gone.

Also what even is adware doctor??????? I haven't heard or known it to be in any way, shape or form an officially recognized and working anti-malware software.

In any case, you have to run a solid anti-malware software, otherwise, it is going to be fairly pointless. Because anti-virus solutions will most likely not protect you against high tier malware offenses or adware. Hopefully, this helps you sort the issue!

Thanks, Josh. I should have stated explicitly I have a Mac. If you have such suggestions for a Mac, I'd be grateful.

Adware Doctor is one of the higher-rated rated malware programs in the Apple App Store. Several user comments called out Mackeeper, which was one of the spam sites my Yahoo mail tab spontaneously goes to. It did identify a plist file, which I trashed, and I no longer see the Mackeeper page. Their customer service person said someone is looking in to my case; we'll see.

In the meantime, while I'm technical, this is well outside my field so I'm grateful for advice from this more knowledgeable community. Questions I can think of now: - Is Bitdefender Virus Scanner free version a great scanner/quarantiner? - Is there an outstanding malware program I should be using?

In my years of the Internet, I've always found MalwareBytes to be one the elite in deleting Malware. I'm sure there's a free trial, or lower "lite" version that's available for free. But I'd definitely recommend it. If you have investments to be made, this software is one, if not the best. https://www.eset.com/us/home/antivirus/

MalwareBytes can be found here: https://www.malwarebytes.com/products/

Malwarebytes especially for MAC OS  :

https://www.malwarebytes.com/mac/

This is almost fun. :^)

Before getting the advice from Zachary and Happy112, my next action was to download and run Antivirus Thor from the Apple Store. It found a bad file and deleted it.

The original problem slowed further but still existed, so I downloaded and ran Malwarebytes as recommended. It identified each of the two other malware programs I installed recently, Antivirus Thor and an element of Adware Doctor. It didn't identify anything else.

Certainly some malware programs are themselves malware, but Apple does vet what goes into their store, so the probability of two random programs being malware is low. So, with all due respect, I'm suspicious of the Malwarebytes results.

Malwarebytes is a hands down trustworthy software. I wouldn't be worried. There are multiple reasons why anti-viruses might detect each other. If they are interacting on the same system level, scanning the files in the same way, or recognize signatures that have an ability to modify files.

Your best bet would probably to check extensions, installed applications, search for suspicious folders manually. I am far less familiar with Mac architecture, so I cannot give you a thorough answer.

Closing the loop on this, the malware is gone, but I had to start from a fresh MacOS install. I restored a few directories from a six-week-old backup, but in most cases I restored individual files saved as email attachments or Dropbox uploads. Then I reinstalled each application I had purchased (I didn't restore the Applications directory); it was nice that no company tried to charge me again.

Sparing the details, I re-loaded everything step-by-step, testing for the problem at each step.

One thing that didn't work was a full restore from that six-week-old backup. At that point I started to fear contaminated backups or router because the suspicious download was far more recent.

As a result of this forum I now use Malwarebytes and the paid version of Bitdefender. They didn't find the malware, but they got enough recommendations that their use seems prudent.

For your amusement: I asked for help from Yahoo and a tech said she couldn't reproduce the problem and asked for a screenshot.

Lesson learned is to be more skeptical of unknown websites and downloads. I don't know for certain that the problem was the Chrome add-on from the Chrome store, but it is the most likely culprit. I'm reasonably technical and yet I fell into this trap, so I wonder how "regular" folks can successfully avoid trouble.

Big thank yous to Josh, FredMcD, Happy12 and Zachary for your advice. You helped me work through the options much faster than I could have on my own. I would have lost far more time without your help.

Glad you sorted out the issue. I have noticed that particularly nasty malware for Macs started spreading about 6 months ago, it could be one of them. For now, complete reinstall usually solves the problems, Additionally, get some form of adblock on your mac, stay safe and best of luck!

Oops ......

I have had this problem from different Yahoo pages for a long time. At one time it was coming from some Publisher's Clearing House pages, but their site has stopped doing it. I've never had the problem from my Yahoo mail page, but I use the "basic" version so maybe the malware hasn't penetrated that one yet. I have been re-directed when scrolling down the Yahoo home page and looking at their news headlines. I was recently redirected from just pulling up the Yahoo home page in another tab; when I switched to that tab it had pulled up the page to download the fake version of Firefox. I am also redirected from Yahoo Finance and My Yahoo. I believe it is related to malicious ads on Yahoo's site. I have run multiple scans with AVG and also Malware Bytes and found nothing wrong on my PC. I've reported this to Yahoo in the past but they haven't done anything; I don't think they care as long as they're getting ad revenue.

Yahoo is just a massive malware spreading nest. While their idea of a search engine wasn't a bad one and intentions were good, the fact is, they couldn't manage their content and security. Which eventually lead to what we have today, not a pleasing experience. By the way, Ajp1228, I would recommend you switch to a different anti-virus solution as AVG has long fallen off the top of the game. Any other free alternative is much better, at least from the popular providers.

Hello. I have this problem now in windows 10. When i am logged in yahoo mail on firefox tab, after a time it jumps to spam sites. I have analyzed my computer with many antivirus: Malwarebits, ADWcleaner, Avast, Bitdefender, Spybot, but I have not found anything. The system seems clean and the problem only happens with yahoo mail (logged) and firefox. I am not able to eliminate this problem. I am concerned about the security of my data. Any solution for this? Thank you.