Installing latest 4.21RFW (REBUG Firmware) will not need Recovery menu, installation was done all through XMB, certified 0% brick unless you were dumb enough or unlucky to brick your console.
Also, about activation stuff on PSN (AKA, Reactpsn) will be manual now, unless someone rewrite the code for reactpsn to work on 4.21CFW, but there's still a way to do it and it's easy:
* Assuming you have 4.21RFW installed and REBUG Toolbox installed.
Run REBUG toolbox, enable REBUG Mode and exit (console will restart)
Create a new dedicated user account on PS3. Then register to PSN.
Download something on PSN that requires activation
Tip: if US account, download Uncharted 2 DLC (it's free BTW) or if Japan account, download Akiba Strip Dynamic Theme (it's free too)
Now you have act.dat residing on your exdata of your current account home folder
Now go ftp and browse over >> dev_hdd0/home/00000XXX/exdata
Tip: the XXX is replacedby any number, just browse over the account who had the current exdata folder with act.dat on it
Backup your precious act.dat somewhere it wont lost, you can use this in the future to pirate PSN Stuff *har
Now dump your IDPS, you will need that also (im not going to tackle about this google it people.)
Now your ready, use the raps file you downloaded over warez sites, convert those files using rap2rif and using the unique files on your console, the IDPS and act.dat you can now activate PSN/DLC/PS1/PS2/Minis stuf
Tip: make sure that the name of the rif file is same with the rap file like
Now on transfer it on your PS3 via FTP or something feasible to transfer the rif file to exdata, where you get the act.dat earlier.
I just knew Rebug would get back to the scene with another CFW, and not only that, but also a bunch of new features giving us more reasons to update. Tested and It's working btw, Rebug stuff are always amazing.
I'll soon try ReActPSN on this, but If you're really worried about compatibility, you might as well stick to 3.55.3 as It can do pretty much everything 4.21 does.