Because of a bug in the Selenium Flex API, it didn’t work with Firefox 3 and the Selenium IDE 1.0 beta 2.
To fix this bug add the following line:
if (flashObj.wrappedJSObject) {
flashObj = flashObj.wrappedJSObject;
}
to ide-extensions.js in Selenium.prototype.callFlexMethod after
var flashObj = selenium.browserbot.findElement(this.flashObjectLocator);