Metagmae.org is a recently reported Browser Hijacker, not necessarily "adware".

Start with this support article: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

A way out of a trap page is to (force it if needed) Close Firefox. Wait about 20 seconds for Firefox to finish closing. Right-click on the Firefox icon and select Open New Window. +++++++++++++++++++++++++++++++++ Sometimes this works. If it opens, close it by Menu > File > Exit. This will flush out that web page from the Session Store.

I doesn't work. It is a terrible malware. I blocked everything about it. But still opens my browser when I start the PC despite it is all blocked.

Hello Memo,

Did you run all malware scans that are mentioned in the article that
the-edmeister gave you a link to ?

Make sure to run all of them, cause what one doesn't pick up; the
other one might.

Also see : https://www.2-spyware.com/remove-metagmae-org.html

And : https://howtoremove.guide/remove-metagmae-org-virus/

Edit : put the last link in brackets to make it clickable.