Comment 12 for bug 166970

It's quite simple. The CSS spec mentions a reference pixel of 90 DPI. There were a lot of internals hardcoded with such ratios. In order to allow for display-dependent zoom to occur, two main things need to happen.

First we need reliable cross-platform code to get accurate DPI info from displays. (This is not always a trivial matter)

Second, we need to change any code left with hardcodings. This is not quite trivial, but does need someone to step up and volunteer to do the work.