Here is extra information about my system:

• Mozilla Firefox Browser 95.0.2 (64-bits) - all Firefox extensions disabled
• Microsoft Windows 10 Home (21H2) Build 19044.1415 (2021-‎07-‎26)
• Microsoft Windows Feature Experience Pack 120.2212.3920.0

Hi Jerome

Which add-ons do you have installed (even if they are turned off)?

I am not suggesting that it is an add-on that is causing this, but something does not look right here.

Have you also tried clearing your browsing history?

Does this happen when you start the browser, or while you are browsing?

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed free to use malware scanners. Each works differently. If one program misses something, another may pick it up.

Hi Seburo, Hi FredMcD,

Thank you for answering my post.

The issue only occurs when Firefox starts. It does not seem to occur while I am browsing.

Here is my complete Firefox extension list:

• Kaspersky Protection
• Link Redirect Trace
• Merriam-Webster Dictionary
• OneTab
• Privacy Badger
• Search by Image
• Signal Spam
• Translate Web Pages
• Undo Close Tab
• Unhook - Remove YouTube Recommended Videos
• Webmail Ad Blocker
• AdGuard AdBlocker
• Antidote
• Bitwarden - Free Password Manager
• Copyfish
• Dark Reader
• Dictionary Anywhere
• Enhancer for YouTube
• ExpressVPN: VPN proxy for a better internet
• Free Download Manager
• Imagus
• IP Address and Domain Information
• IPvFoo

All those extensions are now disabled... And the issue still occurs on every single Firefox start.

My history is cleaned each time Firefox exits. Actually I have set up Firefox to clean everything (history, cookies, passwords...) when it exits.

I have not changed my Firefox settings for a few months. This issue came yesterday out of the blue.

Have you been emailed any files recently that you have saved to your computer?

I am thinking it might not be something in Firefox, but malware on your computer that is "calling out" through the browser.

No. I am very careful about email attached files (and, more generally, about all what is security-related).

Kaspersky Internet Security is always watching my system (emails, browsing, files, OS, network connections, apps...).

During a few minutes I thought I had found the culprit: I use, as a home page, the default Firefox Home with 8 shortcuts in a row. Among those shortcuts, three point to torrent websites. I removed all of them (leaving only the non-suspicious ones) and the issue disappeared.

So I tried to add them, one by one, to get the issue back. Nothing. Firefox now starts without triggering Kaspersky Internet Security... It is nonsense.

I do not know what to say. Now that I am unable to reproduce the problem, the investigation seems to be temporarily dead (until the issue re-appears).

Thanks guys for your help!

No problem, glad to hear it has been resolved.

Well... I am not sure it has been resolved but the issue is gone for now. I will mark this problem as "solved" anyway (maybe it is possible to reopen it if it comes back?)

Happy Christmas Eve guys!