I notice the description of this tool is:
Blocks Processor and Memory attacks of power up to 6.
This suggests that "power" is something different than "intensity". I'm guessing "power" is something along the lines of intensity + code finesse. I definitely got a fractal expansion past a firewall despite it only having an intensity of 1 (when I had 9 code finesse), but that's a bit of a special case since the description of fractal expansion explicitly says that its power increases with code finesse. We should maybe collect data about firewall vs. more standard offensive tools. Also, it might be worth looking to see if hacking opponents have some analog of code finesse themselves, by looking to see if there are cases where they get at tool of intensity < 6 past a firewall.
Important: firewall only blocks memory and processor attacks, not hardening attacks. I know it says that right there in the description, but somehow I had missed that until right about now. I had wondered why it always seemed so useless, and that's why—use it at the beginning of a fight and it's probably not going to do much for you.
EDIT: Oh yeah, this blocks "memory, processor and some special attacks". Which ones?