Adobe Flex Builder, an Integrated Development Environment (IDE) for Flex application uses system default Web browser to running and debugging applications. To change the default Web browser to another Web browser, you can change the workbench Web browser setting which effects how application are run and debugged.
To change default Web browser:
1. Go to Preferences -> Window menu to open Preferences window
Preferences Window
2. Choose Use external Web browser option and select your desired Web browser on available External Web browsers
3. If the desired Web browser doesn’t exists, click New to open Add External Web Browser dialog
Add Dialog
4. Type the name of your external Web browser, eg: Chrome
5. Click Browse to point to your Web browser’s executable file location
6. Click OK to add
7. Select your newly added external Web browser (Chrome) and then click OK to apply
Open your Flex application project and run, your application should be run in the specified Web browser.
by 
That’s a pretty nifty tool, thanks for the heads up I could use some more images for my site.
Thnaks that worked