How remove or change...

Lo resolvi, despues de leer un poco mas, lo resolvi.

1.- ir a FirefoxPortable->Other->Source->FirefoxPortable.ini
2.- Archivo Original:

[FirefoxPortable]
FirefoxDirectory=App\firefox
ProfileDirectory=Data\profile
SettingsDirectory=Data\settings
PluginsDirectory=Data\plugins
FirefoxExecutable=firefox.exe
AdditionalParameters=
LocalHomepage=
DisableSplashScreen=false
AllowMultipleInstances=false
DisableIntelligentStart=false
SkipCompregFix=false
RunLocally=false

# The above options are explained in the included readme.txt
# This INI file is an example only and is not used unless it is placed as described in the included readme.txt

en el archivo original cambian la linia

DisableSplashScreen=false

por esta otra

DisableSplashScreen=true

3.- Copian FirefoxPortable.ini en la raiz de firefox portable

FirefoxPortable->FirefoxPortable.ini

4.- ejecutan firefoxportable