Did you see this guide?

• Remove “Ads by Strong Signal” virus (Easy Removal Guide)

How about trying the removal guide in the following post?

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1.Reset browser settings

2.Disable/Remove Chrome extensions

https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

3. Block pop ups https://support.mozilla.org/en-US/kb/pop-blocker-settings-exceptions-troubleshooting#w_pop-up-blocker-settings

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Here is more information.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

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It’s very sad, but many of the software down-loaders / installers will trick you into installing not only their program, but other programs as well. You have heard of the fine print in shady contracts, right? Well, some installers you need to look at the itsy bitsy teeny weeny fine print. You are thinking you are giving the installer permission to install the program you want by using the recommended option. But if you use the Manual Option Instead, you discover all kinds of stuff that you do not even know what it is or what it does. From now on, everyone needs to Use The Manual Option to put a stop to this.