Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions.

Look for SafeSearch, SearchAssist Incognito, FileConverter Addon, SearchLock, DiscreteSearch, WebSearch, Findwide Search Engine

Now do the same in the computer’s Programs Folder.

Windows: Start > Control Panel > Uninstall Programs. Mac: Open the Applications folder. Linux: Check your user manual.

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.

(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. If you're not sure, feel free to post program names or a screenshot of the list.

(2) Check for a Firefox program folder infection. That would be in one of these locations (varies for 32-bit / 64-bit):

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

A file named channel-prefs.js is normal. Any other file is suspicious. Remove any such files to a neutral location for further analysis at your leisure, or bury them in the Recycle Bin. Please do not double-click .js files as that will execute them as Windows system scripts. You can right-click > Edit or right-click > Open With to view them in Notepad.

If you found a program folder infection, exit Firefox and restart it again before proceeding.

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

• Ctrl+Shift+a (Mac: Command+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 Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. All extensions are optional; the troublemaker might not be obvious from its name.

Any improvement?

(3) You can search for remaining issues with the scanning/cleaning tools listed in this 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.

Hopefully that will flush anything on your system and in your Firefox that could be a problem.

Aqsa97 said

Like the question says, my search engine keeps on changing on its own. I had set it to Google of-course but every time I launch a new window, the search engine changes. I have changed it multiple times, but nothing works. It's not Mozilla's fault btw. I was downloading some softwares earlier this week and I don't know which of the software caused this. I have obviously tried deleting those softwares or anything suspicious but that did me no good. I even reset my Firefox settings and that was of no use either. I have even scanned my entire PC and I found nothing. Can anyone tell me how to get rid of this virus that keeps changing my search engine. And whenever I start Firefox, after every minute my Antivirus (AVG) shows me that it detected a virus/issue and that this was moved to Quarantine. I guess something has infected my browser but I'm not sure how to fix it.

I had already done the 1st and 3rd suggestions before. The 2nd option was what worked for me. Thank you so much sir! :)

FredMcD said

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A) In the Add-ons Manager, on the left, select Extensions. Look for SafeSearch, SearchAssist Incognito, FileConverter Addon, SearchLock, DiscreteSearch, WebSearch, Findwide Search Engine Now do the same in the computer’s Programs Folder. Windows: Start > Control Panel > Uninstall Programs. Mac: Open the Applications folder. Linux: Check your user manual.

The things you mentioned were the first things I did. But they didnt work. However, my problem's solved now. Thank you for your help though!

This could be an issue caused by AdAware or Web Companion from Lavasoft.

Did you find a file named dsengine.js in these locations?

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

You can look for a file named dsengine.cfg in the main Firefox program folder.

C:\Program Files\Mozilla Firefox\
C:\Program Files (x86)\Mozilla Firefox\

Delete the dsengine.js and dsengine.cfg files when present.