HI,
First question that pops in mind mind is whether the application under test supports Firefox.
Did you try browsing to this application using Firefox without TruClient.
1. Open Firefox located in <LR_HOME>\bin\firefox\firefox.exe
2. Browse the applcation nad reach into that point that does not funciton well.
If you face the same issue it probably means your application does not support Firefox. In such case I would advice using TruClient IE
If it works well, I suggest trying again in TruClient Firefox without recording, just browse the application in TC Firefox without recording or replaying a script
Please update us on the outcome
Shlomi