Usually if there is no Remove button, you need to visit the Windows Control Panel, Uninstall a Program. Clicking the "Installed on" column heading is useful in determining whether this snuck in as an undisclosed element of a bundle with something you actually wanted.

Can you track it down there and remove it? Sometimes the names are not obvious (or outright misleading), so consider removing everything you did not intentionally install.

I found a cleanup thread about this extension on a German-language forum, but I don't trust Google Translate enough to suggest any further steps. Instead, check out the specialized cleanup forums listed in our support article "Troubleshoot Firefox issues caused by malware" for further assistance in making sure you've flushed out any lingering unwanted software.

By the way, if you didn't download directly from Mozilla.org and your installer included malware, it would be helpful to report the site where you found it. This might still be in your download history.

I installed Firefox from Moziila.org, so this is not the reason. I had this m.....f.....g Add-On already. No idea from where, Anyway Thanks so far, I 'll check out "Troubleshoot Firefox issues caused by malware"

See also:

• https://developer.mozilla.org/Installing_extensions
• https://developer.mozilla.org/Adding_Extensions_using_the_Windows_Registry

"Download protect 2.2.1" - this is malware on your computer

You can try this malware scanner

ESET® Online Scanner
http://www.eset.com/int/home//products/online-scanner/

and

Malwarebytes Anti-Malware https://www.malwarebytes.org/mwb-download/

problem solved with "malwarebytes anti-malware"

it was "dvtprovd.exe" in c:/win/sys32 which updated the add-on "download protect 2.2.1" everytime it was deleted.

tks again