Mozilla Firefox supports various types of Rich Internet Applications (RIAs), such as Flash, Flex, and Silverlight, via plugins. The plugins have two run modes:
in-process - The plugin runs inside the Firefox process.
out-of-process - The plugin runs in an individual helper process called process-container.exe.
TestComplete shows this message if it detects that the plugin your tested application uses is running out-of-process and in windowed mode.
To resolve the problem, you can do one of the following:
Disable the windowed mode. For instance, to learn how to do that for Flash and Flex applications, see the Configuring Window Mode topic of the Debug Version of Flash Player or of the MSAA Engine section (depending on the approach you use to test Flash and Flex applications).
Use another supported web browser to test your application.