Welcome "Just Users" to the Inter Webs.  ;-)) Can you try booting Windows to Safe Mode and see if you have the same issue?

How to boot in Safe Mode in Windows 10

   Press the Windows logo key + R.
   Type msconfig in the Open box and then select OK.
   Select the Boot tab.
   Under Boot options, clear the Safe boot checkbox.

Thanks for reply. But I don't dare to startup in safemode: I get a popup message about "bitlocker" and that I need a password associated with it next time I want to startup in a normal mode.

But I have never heard of bitlocker and any password associated with it..

This evening, I hate IT

Web search; https://www.bing.com/search?q=bitlocker

You can get the key from the below link and if you don't want your drive encrypted, I would suggest you turn off Bitlocker before it's too late.

https://account.microsoft.com/devices/recoverykey?refd=support.microsoft.com

Is there any content in those tabs ?

You can check that those pages aren't set as multiple homepages.

You can check the homepage setting.

• Settings -> Home
• https://support.mozilla.org/en-US/kb/how-to-set-the-home-page

Firefox supports multiple homepages separated by '|' (pipe) symbols.

You can do a malware scan just to be sure.

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

hello,

when I open firefox once, I only see one tab.

But in task management 8 or 9 versions of firefox are opened... most of them seem inactive (no processor time: 0 %) I noticed this because it took a few seconds before I could type something in the firefox search menu..

the homepage settings, the Microsoft malware scan: no result. And my computer is protected with Norton 360.. the more complicated (the software packages, operating systems etc..), the more problems it seems to me...

thanks.

It is quite normal to see more Firefox processes running.

• process for the main Firefox thread (user interface)
• one or more content processes and with Fission enabled a lot more than before
• process for the compositor thread
• process for extensions
• process for WebRender when this feature is enabled

It is likely you may have Fission enabled in the current release. Fission is about a new site isolation architecture in Firefox and you will see more Firefox processes running than before and when Fission is enabled you can no longer limit the number of content processes in Settings or via dom.ipc.processCount on the about:config page. You can check the current Fission state on the "Help -> More Troubleshooting Information" (about:support) page (search for Fission).

• https://hacks.mozilla.org/2021/05/introducing-firefox-new-site-isolation-security-architecture/

You can find the current multi-process state on the Troubleshooting Information page (about:support).

• "Help -> Troubleshooting Information"
  "Application Basics": Multiprocess Windows
  "Remote Processes" further down

See also the about:memory and about:processes pages for information about the process IDs.