[css3-values][css3-mediaqueries] resolution in dpi / dppx

Hi,

when testing mobile Opera and Firefox browsers, I encountered the 
following inconsistency:

On a device with 2 CSS pixels per device pixel, Opera Mobi 12.10 
reports a media quiery min-resolution of 2ppx or 192dpi. Firefox Mobile 
18.0 on the same device  reports a media quiery min-resolution of about 
3.3ppx or 320dpi. The device is said to have a display with 312ppi. So I 
guess, Firefox rounds 312ppi to 320dpi and calculates

320/96 ~= 3.3 (dppx)

, whereas Opera accepts the 2 CSS pixels per device pixel for 2dppx and 
calculates

2*96 = 192 (dpi)

. Is the Opera version correct and Firefox wrong, because a CSS inch is 
not the same as a physical inch?

-- 
In te domine speravi; non confundar in aeternum
(Te deum, 4th century)