Control panel > Programs > Default programs > Set your default programs.
Open firefox > Click the 3 line icon > Click Options >General > Make default …
Note… If you want firefox on the taskbar you will need to add it , it is not automatically added .
I believe you may have downloaded firefox but did you install it ?
As there is a "Make Firefox default " message upon running firefox until you cancel it..
You can download chrome and install it it will give you the option to make it the default.
You can then keep Firefox or uninstall it
When you first run Firefox, it should ask you if you want to make it your default browser. If not, check its settings, there will be an option there.
on windows type in the search box default programs