@shalym: Provided it's a FW version that actually was available that way at one point (and not OTA-only), yes, it works for me

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TL;DR: You won't be able to get the 2.3.x releases that way, I forgot they were OTA only (2.3 on the other hand, yes, but that doesn't help the OP).
EDIT: On the other hand, the minimal version that the 2.5.8 update supports *is* 2.3, so, as I said initially, the step-by-step isn't useful anyway, so you're not missing anything.
Code:
2.3:
Target OTA 399380047
2.5.8:
Minimum OTA 399380047
Target OTA 555370010