Hi Mister-X, glad to see you on Mozilla Support Forum.

I think you are trying to say that by default your search engine is Google and you want to replace google with some other search engine. You can do that by following way:-

• Click on menu icon.
• Click on options.
• In left pane, you will find search menu, click on it.
• In this menu, you will find Default search engine option.
• Click on Google as shown in picture, a dropdown menu will be open.
• Then, just choose your favourite search engine.

If it doesn't solved your problem, then feel free to ask in Reply Section. Thanks for raising your question in Mozilla Support Forum.

I need the solution in about:config or in other files

Thanks

Hello   Mister-X,

You seem to be dead set on enabling/disabling/removing items via the about:config page, while you can easily do these things otherwise, like in this case :
highlight a search engine and click "Remove".....

(in another thread you also want to enable the bookmarks toolbar via about:config)

Your screenshot shows that your browser is being managed by your organization;   is that intentional ?

Yes, we plan to roll out firefox in our company, with mozilla.cfg so I'm asking you unfortunately I have to ask many questions here, because I have not found in the internet

Unless somebody here comes up with answers that you are looking for;
maybe you could consider posting on this support forum (for Enterprise) :

https://support.mozilla.org/en-US/questions/new/firefox-enterprise/form

(just a suggestion)

Maybe these articles will interest you :

https://support.mozilla.org/en-US/kb/customizing-firefox-using-autoconfig

https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Enterprise_deployment

https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson