It's likely caused by an app installed on your computer outside of Firefox. You should look to make sure that you don't have any suspicious apps installed on your computer.

Additionally, it may be a good idea to scan your computer for malware using a scanning program. Malwarebytes makes a good program for Mac computers, which should detect most issues.

Hope this helps.

Try the malware removal programs listed here https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware#w_how-do-i-get-rid-of-malware_2

Not all malware removers will catch everything so you may have to try a couple of them.

EDIT: Whoops this article doesn't display "Malware removal programs" if you're on a mac. I'm gonna leave it incase a windows user finds this post. Thanks Wesley!

Thanks for the replies. I did try Malwarebytes but the problem still exists.

Have you tried changing the Firefox home page? If that page was set as your home page, that would explain why Firefox is opening that page when you start.

Hi I have this problem too. When I open Firefox, it opens a tab with the Anysearch search engine. I have checked my preferences and DuckDuckGo is correctly selected as my default search engine. Firefox is correctly selected as my default browser. If I open a new tab once Firefox is running, it selects the correct search engine, but it concerns me that Anysearch is still on my computer in any way.

I tried Malwarebytes and it did not remove the problem. I even wrote to Malwarebytes and they sent me a patch to run, which did not correct the problem. Help?