Many thanks phiber
I think that Cydia must remove the "Make my life easier" option after we've selected it once. And I must have selected it ages ago.
I'm lost when you refer to iOS and firmware 4.2.1. Trying to unscramble terms, I think the iOS is firmware. Not to be confused with Modem firmware, otherwise know as baseband. These terms are used chaotically all over the place, so I find one needs to do a lot of guess work and turning of blind eyes.
So you should be able to install any iOS version that you have SHSHs for, plus the current version 4.3.3 (Apple will issue the appropriate SHSH).
However beware of one thing that caught me out. Various sites said it was safe for me to update my iOS to version 4.1, which I did. Only to discover that my baseband was changed to 05.14.02, which cannot be unlocked.
There are apparently ways to install some iOS versions without changing the modem baseband. I haven't dug into that yet. UltrasnOw warns not to use redsnOw as it updates the baseband, I didn't use redsnOw but was nuked anyway.
The reason I started jail breaking at all is that this is an iPhone given me by an American friend and I am in Europe so can't use that US phone carrier here. Since then I relish the culture outside Apple control-freak walled garden.
Anyway getting back to your iPhone, if I understand you right, you just want to get the latest firmware, not jailbroken. That should be easy, just use the standard iTunes installer, but be warned it will completely erase everything that you currently have on your phone, so make sure you have backups.
I think Apple's default approach is to allow you to install the current iOS anytime, but in doing so lose any jailbreak material.
Further confusion decryption efforts: Restore Mode mode is not the same as Recovery mode. Also "restore" = reinstall the iOS, while "reset" = erase personal data.
Of course I am struggling in all this to understand both the technology, ethos, and lingo that drives this iOS world. I find the chaos of kidspeak and youtube egofest material one heck of a compost heap. Still at least it helps me get a small sense of the way the world is and slow Alzheimers..
I'm sure eventually I'll stumble upon some who have both wide comprehension of the issues and powers of communication. As it is, for every possible fact-let, there are hundreds of assumptions which I do not share with whomever presumes them. One needs a style filter to thin the chaff out.
The above just by way of saying that I don't trust me yet in iPhonery, and you certainly should not. But I'm trying!