Firefox 3 introduced a new bug, which causes Flash to ignore the local keyboard layout (ie. deDE) in input fields like a textbox. Instead it uses the default: enUS.

This problem occurs if you set the parameter „wmode“ to „opaque“ or „transparent“. Removing that parameter fixes the problem.

The problem is: if wmode is not set to opaque, you cannot debug your flash application with Flex Builder 3 and Firefox 3. So, now you have to choose what you want to achieve. Or switch the parameter before publishing a new release.