Where did you get the initial download? Unfortunately, search engines allow misleading ads from bundlers to masquerade as the real thing.

Download page: https://www.mozilla.org/firefox/new/

And to clean up any other junk:

(For Windows Vista, 7, 8, 8.1, 10; 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 should surface undisclosed bundle items that snuck in with the 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.

(3) Supplement your regular security software using 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.

Firefox for WIndows, Mac OSX, and Linux from www.mozilla.org www.mozilla.org/firefox/all does not come with any form of trojans, viruses, adware, malware, bundled apps, etc. It is only Firefox you get.

Just because you see something suspicious in Firefox or on OS after a Firefox install on Windows does not mean the official Firefox versions came with such.

Some download sites such as cnet aka download .com is a known adware site that often bundles extras with otherwise clean software.

https://malwaretips.com/blogs/one-system-care-removal/

Thank you, jscher2000 and James!

I checked my history, and I had actually downloaded from open-download.com. It was the first result listed in my search for Firefox, so I had assumed that it was the correct site. Big mistake. I was able to uninstall One SystemCare, and hope that there are no additional add-ons on my computer.

Thanks again! Schreibs

Schreibs said

I checked my history, and I had actually downloaded from open-download.com. It was the first result listed in my search for Firefox, so I had assumed that it was the correct site.

Some search engine sites like Google and Bing can sometimes have Ad links above the Real search results. These Ad links can sometimes lead to questionable sites instead of its homepage.