Why does the Google search engine pop up when I’m trying to use Firefox?

What's so strange about it? Firefox is a browser and Google is a search engine. Two different things.

In Firefox's Settings you can switch the search engine to whatever you want.

Why does the Google search engine keep popping up when I am trying to use Firefox

https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox

Because you have Google set as the default search engine in the Firefox web browser.

You can change or install another search engine to use in the desktop Firefox web browser as shown in the KB article link. A search engine is for example qwant.com, duckduckgo.com, bing.com etc.

Mozilla the makers of the Firefox web browsers does not have a search engine site of their own.