n Firefox go to Tools > Options and click general tab. Under the Default Browser section click "check now". Firefox will ask if you want default browser. Click Yes. Also check the box so that Firefox will check to see if it's the default browser when you start it up.
You right-click your task bar(that is the bar that has the start menu). Then you click properties and go to the start menu tab. You then press the customize button right next to start menu, after u choose what browser you want to use where it says internet explorer
go to tools bar in the Firefox,click on options,click on advanced tab, tick the box under system defaults,and click on check now button,if Firefox is not set as default browser,we can set now by clicking on yes