Sadly, I have already tried all of this. firmware.bin downloaded just fine with python 2.7, and the mset hack installed just fine as well. I also tried to launch with the browser but the same thing happens.
What i did to make my 4.1 JPN O3DS work:
1. [GW] install gw mset with DS cart.
2. [GW] from mset, back up NAND, format emunand.
.. [PBT] Well i used to install the PBT to get devMenu.. Quite boring, and doesn't need now.
.. What i had to use is RxTools 2.4, 2.5.2.
3. [rx24] Install rx mset. and use which cdn_firm.py that rxtools 2.4 offers to get the old firmware.bin (943KB).
4. [rx24] from mset, launch emunand. then update it to latest.
5. [rx24] from PC, i backup emunand, and collected nand.bin.
6. [rx24] get the nand.fat16.xorpad, which could be used to decrypt nand partition.
.. rx 2.4 and 2.5 are similar.
7. [rx26] Get the latest release package from github.com. size 12.1MB. delete rxTools folder inside SD.
8. [rx26] get firmware.bin (new, 3MB+) with the cdn_firm.py included in the package. get both file to card.
9. [rx26] Wait for quite a minute or so to install rx decrypted+patched files. launched the emunand.
It is said that you must ever install GW mset and run GW classic mode, so then you can get rx one running. I don't know why and not sure about it.
Well right. if press R to enter menu then start emunand, it does boot. Sometime it isn't stable enough.