try these instructions:
Firefox: " Tools -> Options ->General -> Default Browser -> Check Now"
If that doesn't work, try setting ie as the default browser, then (re)set Firefox or Mozilla Suite as the default.
If that still does not work, try this:
Setting default browser manually
* In Windows XP, go to "Start -> Control Panel -> Add/Remove Programs -> Set Program Access and Defaults (on the left) -> Custom". After expanding the "Custom" category, you will see Internet Explorer and other installed browsers listed under "Choose a default Web browser". Select Mozilla or Mozilla Firefox.
If that doesn't work,
* In Windows Control Panel and if Windows XP is using the Control Panel "Classic View":
o Click on "Folder Options -> File Types".
* In Windows XP using the Control Panel "Category View":
o Click on "Performance and Maintenance". Then, click on "File Types" in the left column under the heading "See Also".
Assign the following filetypes to the browser you wish to set as default:
* URL:HyperText Transfer Protocol
* URL:HyperText Transfer Protocol with Privacy
* URL:File Transfer Protocol
* HTML File
* HTM File (optional)
Note that you may find the URL file types above under extension "N/A" or "(none)".
all article here