Yeah, all the windows in mIRC will have that font setting.
It's worth noting that the negative use of the fontsize (-12) should, according to the help file, match the size in the /font dialog, which as we just saw, only has '9', or maybe '11' for you, still, it's not 12, so there is an issue somewhere.
tried your command and it indeed made it larger, however, doesn't seem to be fixedsys font...kinda looks more like arial. tried it with the -11 and youre right..that drops it back to fixedsys 9
tried the command with -10 and although its listed as 10 it actually looks more like 9
