If I understand your question correctly, I think you want to be sure you make Mozilla Firefox your "default browser" for whatever Operating System you have on your computer.. For example, I have a Windows computer, so Windows is the Operating System of my computer, & Microsoft Windows is always trying different ways to get you to use their own "Edge" browser, & to get you use their own "Bing" search engine. But thankfully for someone like me, who most definitely prefers to use Mozilla Firefox as my browser, & DuckDuckGo as my search engine, Microsoft Windows doesn't actually FORCE you to use either their own Edge browser or their own Bing search engine, & they make "not too difficult" ways available for someone like me to make Mozilla Firefox my "default browser", & to make DuckDuckGo my "default search engine" on my Windows computer.. HOWEVER, based on what you said in your question, I think you may have an insurmountable problem with a computer you may be owning & using, because my understanding is that at least the Operating Systems that come with some computers DO actually FORCE you to use only their own browser, which comes installed with their computers that are sold [& maybe also FORCE you to use their own search engines too, though I'm not absolutely sure about that.]. But where I think you "may" have a problem "without a practical solution" is that the one kind of computer I know of, where my understanding is that the computer DOES force you to use their own browser they're inextricably connected to, where the company making & running the browser is the same company directly involved with the making & selling & marketing of those computers, is Google Chrome, because the one specific situation like that, that I'm aware of, has to do with those Google Chrome little "Chromebook" very small computers, which according to my understanding actually DO in fact FORCE you to have to use the Google Chrome browser that comes with the computer, where they don't give you any option to switch over to Mozilla Firefox or any other browser on those little Google Chromebook computers. Perhaps there are other larger sized computers where the manufacturer also has a very direct connection to Google Chrome, & also doesn't give you an option of switching from the Google Chrome browser, though I don't know about that. And I've never owned an Apple computer & really know virtually nothing about them, though I do know they have their own Operating Systems, so maybe Apple computers don't let you use a Mozilla Firefox browser either, though, once again, I'm not completely sure of that. Anyway, friend, I hope at least something I wrote here may be of help to you, because I've certainly SPENT ENOUGH TIME in writing this ! : - ) In any case, GOOD LUCK !, friend, with your present situation ! : - )

I want to be browsing using the Mozilla browser

You appear to be using the Mozilla Firefox or Firefox for short web browser just fine to post this support forum thread.

Note that Firefox is a web browser and not a website nor a search engine. The mention of Chrome I am guessing you are referring to the Google search engine in Firefox?

If this is about making Firefox the default web browser on Windows. https://support.mozilla.org/en-US/kb/how-change-your-default-browser-firefox-windows

If this is about the search engines in Firefox. https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox https://support.mozilla.org/en-US/kb/add-custom-search-engine-firefox https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox