BAT file opens Default Browser instead of Firefox

I have a login script that runs for every user. The first check sees if the useame matches our Test-Taking User (exam). If so, launches Firefox to the exam homepage and stops.

The commands individually work. When I call the .bat file, it launches Inteet Explorer to the website. What am I doing wrong?

@echo off

REM Exam Startup - Useame is "exam", then start the Exam website, and exit the script
if %USERNAME% EQU exam (
    if exist "%PROGRAMFILES%Mozilla Firefoxfirefox.exe"       start "%PROGRAMFILES%Mozilla Firefoxfirefox.exe" "https://www.example.com/"
    if exist "%PROGRAMFILES(x86)%Mozilla Firefoxfirefox.exe"  start "%PROGRAMFILES(x86)%Mozilla Firefoxfirefox.exe" "https://www.example.com/"
    exit
)
...
REM rest of script