Firefox downloaded on my brand new iPhone 11 Pro but iOS doesn't see it nor opens anything through it

I just bought a new iPhone 11 Pro with the latest iOS version installed and successfully downloaded Firefox app and installed it. Whenever I try to open a link to an online tool that only works with Firefox (Coach), the system asks me if I would like to open it in Safari and Google (it doesn't give me the chance to open it in Firefox). Of course when I open it in one of those browsers, the system tells me that it cannot open the to and asks me to download Firefox app while it is already installed. The same happens when I open directly Firefox app nand try to use it as a browser to search things, it tells me to download it and takes me to the starting point. I also disinstalled Firefox and re-installed it, but the issue persists. Any suggestions?