Does the home page --

• stay changed until you exit Firefox and start it up again?
• stay changed until you shut down Windows and start it up again?
• change back shortly after you change it?
• not change at all (i.e., you go back into Options and it's wrong again)?

There may be some active component still on your system after your cleanup. Here's my suggested procedure for tracking down and cleaning up bad add-ons and other hijackers. I know it seems long, but it's really not that bad.

(For Windows Vista, 7, 8, 8.1; XP is somewhat different)

(1) Open the Windows Control Panel, Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it. Take out as much trash as possible here.

(2) Open Firefox's Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons
• in the Windows "Run" dialog, type or paste
  firefox.exe "about:addons"

In the left column, click Plugins. Set nonessential and unrecognized plugins to "Never Activate".

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. All extensions are optional; none come with Firefox.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

(3) You can search for remaining issues with the scanning/cleaning tools listed in our support article: Troubleshoot Firefox issues caused by malware. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case.

Two other things to check after the initial cleanup:

(4) Is there any user.js file?

Firefox allows an optional settings file named user.js to override your saved preferences from the previous session at startup. Unless you created that file yourself, it may contains settings from an add-on or external software. You can check and remove the file using the steps in this article: How to fix preferences that won't save.

Note: by default, Windows hides the .js file extension. To work with files as accurately as possible, I suggest showing all file extensions. This Microsoft support article has the steps: http://windows.microsoft.com/en-us/wi.../show-hide-file-name-extensions.

(5) Make sure your Firefox shortcut is clean.

Double-check the shortcut you use to start Firefox. Either:

• Desktop shortcut: right-click the icon, choose Properties
• Pinned taskbar icon: right-click the icon, right-click Mozilla Firefox, choose Properties

Windows normally will select the Shortcut tab. If not, go ahead and click the Shortcut tab.

The Target line should not have anything after this part:

• 64-bit Windows, standard 32-bit Firefox: "C:\Program Files (x86)\Mozilla Firefox\firefox.exe"
• Otherwise: "C:\Program Files\Mozilla Firefox\firefox.exe"

If any URLs are listed after that, clear them out and save your change. To test, you can either:

• Desktop shortcut: double-click the icon to launch a new window
• Pinned taskbar icon: right-click the icon, click Mozilla Firefox to launch a new window

If you get your home page, it worked.

Some users have reported a faster fix for a pinned taskbar item:

• unpin the current icon
• go into the Start menu, right-click Mozilla Firefox, then Pin to Taskbar

Any improvement?

Hi

Thanks for the response.

It reverts to the unwanted default shortly after I've chnaged it. I don't have to exit Firefox for this to happen.

I'm on win 10.. I assume your recomendations stil hold..

This all started after installing the VLC media viewer, which has now been uninstalled.

I've done the other things you suggest, including scanning with all four malware seekers, as well as windows defender.

A search in windows explorer for a user.js file threw up a user.js.vir file held in the ADW cleaner quarantine. But I'm still getting the problem.

And I've checked the shortcut too... all fine.

Arrgh..

In case there is a memory-resident component that is preventing removal, you also could try the clean-up again in Windows' "Safe Mode with Networking" mode which limits what can start up automatically.

http://windows.microsoft.com/en-us/windows-10/start-your-pc-in-safe-mode

Some extensions have a "self-hiding" function. Could you cross check the list on the support information page for any unknown/unnecessary extensions. Either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

Scroll down to the Extensions heading and review the table that follows it. You also can copy paste from that section of the page into a reply (it will look a little messy, but we're used to it).

If anything additional shows up here that wasn't on the Add-ons page, you can try removing it in Firefox's Safe Mode, where self-hiding isn't possible:

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: 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

and OK the restart.

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

Then return to the Add-ons page as before.

If it's not an extension, it could be a program folder infection. These are unusual but have been seen in some cases. For that, I suggest:

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. Do NOT uninstall Firefox, that's not needed.

(A) Download a fresh installer for Firefox 44.0 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(B) Exit out of Firefox (if applicable).

(C) Rename the program folder as follows:

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.

Does a cleanly reinstalled Firefox "bookmark all tabs" normally??

Note: Some plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

OK, I need to go and eat now [early evening here in the UK]. I'll run through this later and let you know. Again, thanks for your help. David

Right. There's an extension called 'Search.Know'. I had disabled it as I didn't know it. But you were right. I should have removed it. I've done so now, and the problem has ceased. Thanks for your help.

David

Err, sorry, I was wrong. The nature of the probem has changed. Now the default search engine that I set up in options remains correct. But if I enter a search term in the url address bar, Malwarebytes blocks the subsequent page as the search isn't actually taking place using my default search engine, but the malware one. So I'll have a go at your last suggestions...

Here is the list of extensions that you asked for: Extensions Name Version Enabled ID Adblock Plus 2.7.1 true {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d} Ecosia — The search engine that plants trees! 3.4.2 true {d04b0b40-3dab-4f0b-97a6-04ec3eddbfb0} Internote 3.0.2.1-signed true {e3631030-7c02-11da-a72b-0800200c9a66} Kifi Knowledge Keeper 3.5.7 true kifi@42go.com Logitech SetPoint 6.5 true {F003DA68-8256-4b37-A6C4-350FA04494DF} Prostetnic Highlighter 2.0.5.1-signed true jid0-pJMJEntDZuwYnkFvfCcFQsgmvBY@jetpack

OK, I've done a clean reinstall. No change I'm afraid.

OK, I think I've cracked it. I booted up in safe mode and ran Malwarebytes. It found a nasty in firefox profiles, which I deleted. Now everything seems to be alright. Fingers crossed!