I have used the Flex Application with IE. Now I have change Browser and make it Firefox.
There are two steps.
1) First Select Menu—> windows –> Preferences –> General –> Web Browser…
After that you may able to change the browser.
2) Go to Command Prompt and type
––> ftype http=”c:\Program Files\Mozilla Firefox\firefox.exe”
Reopen Flex Application.
Now run your application then browser is changed.