If there is a problem, and you use sync, the problem may spread thru the sync. Disable sync. Fix the issue. Then check the other computers for that problem.

That was a major issue that seriously concerned me, and just proved something I will not trust in again, obviously turned off - nice thought\feature though. What and how does one fix the issue moving forwards?? As becoming very tedious and although a fan and user of Firefox for untold years will look elsewhere if my browser is being hijacked every couple of days!!!

There's no way that anything will "hijack" a Sync process. The connection between Firefox and the Sync server is encrypted via the HTTPS protocol and the Sync data itself is encrypted whenever that data is not in Firefox - that Sync data sits on the Sync server encrypted and only your Firefox installation has both "encryption keys' - kA and kB. Not even Mozilla can break that encryption.

Any chance that your Internet Service Provider has any "relationship" with Yahoo?

Some ISP's have been doing DNS redirects in recent years to pickup a fraction of one-cent per redirect in royalties for redirecting searches to their "partner in crime" - $100 / month for broadband service and they "come into our homes to vacuum pennies from out of the couch" - that is a "crime" and that's an action reserved toddlers in our families for their piggy-bank. https://en.wikipedia.org/wiki/DNS_hijacking#Manipulation_by_ISPs

Please explain why you say that Yahoo has "hijacked" your searches in Firefox. Could be a Malware issue - but I'm not proficient with MacOSX to even begin to help you.

Every couple of days my browsers home page and search criteria go from the 'default' google to yahoo, when it 1st started I removed yahoo as an option in preferences but still seeing yahoo "hijacking" the browser settings even though no longer an option. My reference earlier regarding sync, was if it can manipulate browser settings what's stopping it going one step further?? A rhetorical point that they have gone this far, whats next..... To my knowledge my ISP has no affiliations - I will double check tomorrow. Unlikely Malware but will look into later.

I tried all the obvious "solutions" and none worked. Changing settings in Firefox does nothing. Using the latest version of firefox does nothing to change the problem. Currently running FF 43.0.1 and Win 10.

I like all the cute simple answers but this is beyond everything I have seen here. I notice that the yahoo serch bar can only be removed one character at a time. Take forever and holding down the delete key only removes one character.

I have been building Opera to the way I like it and will switch to that permanently if I can't fix the yahoo problem. I do not trust Yahoo and will never trust yahoo. Unfortunately, I am beginning to not trust firefox either. No more donations unless this can be fixed. It is a serious problem as microsoft draws the rope around all my email accounts and actually has started sending my business email to my personal account. Really intrusive and proof that not trusting is safer.

So, if anyone has any solution please tell me. I have already done everythign I found on here and nothing has worked.

Please!

Have since moved to Safari (Mac user) and so far no problem, a shame as have always liked\trusted Firefox until recently

I have this problem too. It is driving me crazy. I keep hoping that the next version of Firefox will fix this issue.

I also have this problem. I am not using Sync. The problem appeared after Yahoo! updated their toolbar (and eliminated everything I had added). Now every time I click on a link it opens a new window and a new tab. The new tab is Yahoo search. It had also disabled Firefox options and add-ons. I am using Time Warner RoadRunner. I do not know if the have any kind of agreement with each other, but what Yahoo is doing is not okay with me. Of course they do not respond to complaints.