Deliberate mistake: When Harrison Ford and Mary Lynn Rajskub are crossing the tracks, its Rajskub who's driving the car, not Ford. This is because the filmmakers originally had Rajskub driving the entire way. They later refilmed the drive with Ford driving, but kept the shot of them crossing the tracks the same. Ford and director Richard Loncraine confirm this on the special features of the DVD.
Firewall (2006)
1 deliberate mistake - chronological order
Directed by: Richard Loncraine
Starring: Harrison Ford, Paul Bettany, Virginia Madsen, Jimmy Bennett, Carly Schroeder
Factual error: When Janet dials 911 from her cell phone, we hear a low tone followed by two higher tones. In reality, 911 is a high tone followed by two lower tones. Additionally, she dials 911 and puts the phone up to her ear without ever pressing the "Talk" button. (01:35:10)
Jack Stanfield: Change of plans, asshole: You get the money when I get my family.