Could you check the following:

(1) Was a new search engine installed and made your default? Check this article for how to change it back to your preferred search site: Change your default search settings in Firefox.

If that works temporarily but does not stick -- it changes back immediately, or it changes back when you exit and restart Firefox -- then we'll need to help you track down the source of that.

If that doesn't work at all and is ignored, what is the name of the new search engine?

(2) Were any new extensions installed? You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything related to Ad-Aware, or searching? Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?

(3) Have any Policies been enabled? To view active policies, type or paste about:policies in the address bar and press Enter to load the page.

The normal content of this page is: "The Enterprise Policies service is inactive."

If you have anything here, it could be injected using either the Windows Registry or a file. Let us know what you see, especially if it's search-related.

1.The search engine set as"default search engine"I tried to change it to Google-it doesn't helped.The "Ad Aware"shows up periodically,not each time. 2.and3. I checked like you said-did find nothing suspicious.

1.The search engine set as"default search engine"I tried to change it to Google-it doesn't helped.The "Ad Aware"shows up periodically,not each time.

Could you check for an Autoconfig file. This is a little difficult to describe because the file name can vary, but here is where you can check for it. Either:

• C:\Program Files\Mozilla Firefox\defaults\pref
• C:\Program Files (x86)\Mozilla Firefox\defaults\pref

Normally, there is only one file in this folder, named channel-pref.js -- any other file here is suspicious and could be a mechanism to override your settings. Anything?

2.and3. I checked like you said-did find nothing suspicious.

To see whether the problem is caused by a non-suspicious extension, you could test in Firefox's Safe Mode. In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

If Firefox is running: You can restart Firefox in Safe Mode using either:

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

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Did exactly what you said-nothing helps.Its still there.

So at this point, what is happening:

• Cannot change back to Google
• Can change back to Google but searches are hijacked anyway
• Can change back to Google but it reverts to the unwanted search engine at the next restart

Also, did you delete the unwanted search engine from the One-Click Search Engines box further down on the Search panel of the Options page?

If the unwanted search engine is not getting re-injected by an extension, Policy, or Autoconfig file, it may be coming from other software/malware running on your system.