Nice, I tweaked it to make http://jsfiddle.net/UPBUH/7/ , you can see what your browser + O.S. picks for each font name in the font stack.

I get the same.

FWIW Chromium does something different for me, it's matching Helvetica but not using Nimbus Sans L. something more like Liberation Sans.

 

 we're saying we want to use that free font (because it's a free, and fits our intended design well).

If it's as good or better than Helvetica Neue, I think everyone agrees the free font should come first. Yo, designers...? I think Quim goes further to argue our sans-serif font list should be
   "Nimbus Sans L", "Liberation Sans", sans-serif

I have no idea what that font stack does on Windows/Mac/iOS/Android. It's the last thing in http://jsfiddle.net/UPBUH/7/ , can people report back?

Kaldari:
"Nimbus Sans L" is the files n019003l.{afm,pfb,pfm} in http://packages.ubuntu.com/saucy/all/gsfonts/download , the command to extract one file is
   $ dpkg --fsys-tarfile /path/to/gsfonts_blahblah.deb | tar xOf - ./usr/share/fonts/type1/gsfonts/n019003l.pfb > /tmp/NimbusSansL.pfb

and I sent the files to you on a 3 1/2" floppy ☺

Cheers,