[TYPO3-mvc] Switch storage backend in FE context

[Torsten Schrade]

Dear list,

I'm trying to override some methods in the standard Typo3DbBackend. 
Currently I register my own storage backend by doing

config.tx_extbase.objects {
	TYPO3\CMS\Extbase\Persistence\Generic\Storage\BackendInterface {
		className = MY\Extension\Persistence\Generic\Storage\PatchedTypo3DbBackend
	}
}

In a BE context this works absolutely fine. But strangely enough it 
doesn't work for me in a FE context. Somehow my class doesn't seem to 
get called, only the standard backend class is executed… Can you direct 
me to a good entry point for debugging why the TypoScript configuration 
doesn't seem to work in my FE?

Thanks a lot and best regards,
Torsten