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Opening Firefox results in antivirus URL:blacklist warning blocked connection to http://site-great.xyz from proces: C:\program files\Mozilla firefox\firefox.exe

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When I start Firefox (Windows10) on my desktop computer. My anti-virus (Avast webshield) blocks a connection to a malicious site (see image for full link). from the process: C:\program files\Mozilla firefox\firefox.exe.

Running intense anti-virus scans on my computer results in "nothing found" also a scan on the Mozilla firefox doesn't show anything found. I have uninstalled Firefox and downloaded/installed a new version of Firefox but the problem still exists. Firefox keeps blocking a popup window which links to this site: https://eronqusa.ru/c/?quid=55(....etc.etc.) Possible mail.ru virus? I also manually removed a folder SCRSNAP by deleting it from %users\appdata\local on my C:\ drive (although I haven't restarted my pc yet, so it might return)

I hope this info helps a bit, if you need more info just let me know. Thanks in advance.

When I start Firefox (Windows10) on my desktop computer. My anti-virus (Avast webshield) blocks a connection to a malicious site (see image for full link). from the process: C:\program files\Mozilla firefox\firefox.exe. Running intense anti-virus scans on my computer results in "nothing found" also a scan on the Mozilla firefox doesn't show anything found. I have uninstalled Firefox and downloaded/installed a new version of Firefox but the problem still exists. Firefox keeps blocking a popup window which links to this site: https://eronqusa.ru/c/?quid=55(....etc.etc.) Possible mail.ru virus? I also manually removed a folder SCRSNAP by deleting it from %users\appdata\local on my C:\ drive (although I haven't restarted my pc yet, so it might return) I hope this info helps a bit, if you need more info just let me know. Thanks in advance.
Attached screenshots

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You can try these free programs to scan for malware, which will work with your existing antivirus software:

Microsoft Safety Scanner https://docs.microsoft.com/en-us/windows/security/ threat-protection/intelligence/safety-scanner-download

MalwareBytes Anti-Malware https://www.malwarebytes.com/premium/

Anti-Rootkit Utility - TDSSKiller https://www.bleepingcomputer.com/download/tdsskiller/

MalwareBytes AdwCleaner https://www.malwarebytes.com/adwcleaner/

ESET Online Scanner https://www.eset.com/us/home/online-scanner/

(Malwarebytes Chameleon - allows installation of Malwarebytes on an infected system https://www.malwarebytes.com/chameleon/)

Running more than one or all of the above mentioned Scan Tools is recommended since they scan at different levels of your computer. And, of course, run the scans with Firefox Closed.

Also: Troubleshoot Firefox issues caused by malware

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Some tools did detect threats on my system, and placed them in quarantine. FireFox is slower now when opening websites, but that is probably scanning the websites first before opening. I can live with that. The error message URL:Blacklist is gone now and no more blocked pop-ups by firefox.

Thanks!!!

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I'm glad to hear that you found the culprit and are rid of it.

Regarding the slowdown, some anti-virus programs don't work well with each other and having multiple programs installed at the same time can cause that problem. For example, if you installed Malwarebytes for the first time, and have the trial Premium version installed, it may be causing a conflict with another program.

There are some other tips in this article, which may help speed things up: Quick fixes if your Firefox slows down https://support.mozilla.org/en-US/kb/quick-fixes-if-your-firefox-slows-down