Does the home page change when you check that in "Options > General > Startup" or is this a problem with the page that opens when you start Firefox? For the latter you can check the target field in the Firefox desktop shortcut.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

If you do not keep changes after a restart or otherwise have problems with preferences, see:

• http://kb.mozillazine.org/Preferences_not_saved

Do a malware check with several malware scanning programs on the Windows computer. Please scan with all programs because each program detects different malware. All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

? SOLUTION ? I wasted three hours last night trying to sget rid of the Yahoo home page. Just now I uninstalled Adobe Air and some superfluous unknown interloper with "hold" in its name; I had to restart after. When Windows restarted there was a notification that there was a new version of Firefox, which I installed.

One of these three items presumably caused the Yahoo! glitch.

One other thing I did: I did not make Firefox my default browser. (I haven't yet tried to make it my default browser, so I don't know if that might make the problem re-appear.)

Hi johnbarr, I noticed you posted in two different threads, but you were not very specific about what you have tried so far.

Firefox 34 was released on Dec. 1, 2014, so unless you have been waiting to update, it's very likely that you already had it and that the prompt to update was bogus.

Have you already run the suggested malware scans (see earlier posts)?

Have you tried ruling out a bad extension by testing in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

I spent three hours trying to get rid of the Yahoo! homepage before I gave up and uninstalled Firefox and started full use of Internet Explorer as my browser. Included in my attempts were the three normal ways of specifying my own home page (Outlook) in various combinations. Exactly what did others do that solved this problem? Your list of things to try was so long that I would still be trying things if I hadn't given up.

My Firefox version is 34.05.

Later, after my wife complained about not having Firefox, I re-installed it. It still had the hijacking bug. Then I did four things, one of which cured the problem: 1) uninstalled Adobe Air; 2) uninstalled a program which had "hold" somewhere in its name; 3) got a message about an upgrade to Mozilla or Firefox being available, 4) So I followed the link, installing Firefox. I declined everything except Firefox and did NOT make Firefox my default browser.

Result: no more Yahoo! home page.

I will try your safe mode suggestion if the problem returns. I did try safe mode once, but did not have the detailed instructions you gave above.

Hi johnbarr, I didn't realize you had already solved the problem before you posted. Thanks for reporting back.

It isn't a solution. A solution is when everyone knows 1) the source of the problem, and 2) the specific fix, and 3) then Firefox makes it impossible to hijack my home page.

Hi johnbarr, it's unlikely I can determine #1 and #2 at this point since the problem has gone away. If it recurs, I'll have some suggestions for tracking it down.

As for #3:

• Firefox allows add-ons to override your home page setting. I don't think that is likely to be blocked because in some cases, that is useful.

• Windows also allows third party processes to modify your program shortcuts to launch a web address or document. Firefox will faithfully load that instead of your home page. But in case of this kind of hijack, the Home icon or Alt+Home keyboard shortcut usually still work normally.

RE: "Firefox allows add-ons to override your home page setting. I don't think that is likely to be blocked because in some cases, that is useful."

Is it a Product Improvement or a Bug Fix to give me the option to have Firefox not allow add-ons to override my home page setting?

I don't understand much about add-ons. Perhaps Firefox should keep and make available a table of add-ons together with the things those add-ons do to Firefox as an environment.

Hi johnbarr, please start a new question for further discussion since the original poster has marked this one as solved.

For more information on viewing and managing your add-ons in Firefox, see:

• Find and install add-ons to add features to Firefox (you'll notice there are several categories of add-ons on the page, the most important are Plugins and Extensions)

Thank you for the support. I expect studying "add-ons" will be helpful to me.

Ps: The hijacking of my home page by Yahoo! has not yet happened again.