Make sure you set up the directory like this:
firefox
| - firefox.nuspec
| - tools
| - chocolateyInstall.ps1
| - firefox.ini
| - 32bitinstaller.exe
| - 32bitinstaller.exe.ignore (shim director, empty file that bears exact name of exe with `.ignore` appended)
| - 64bitinstaller.exe
| - 64bitinstaller.exe.ignore (shim director, empty file that bears exact name of exe with `.ignore` appended)