Text rendering allows font fingerprinting

Using dcf's font fingerprinting demo,

https://www.bamsoftware.com/talks/fc15-fontfp/fontfp.html#demo

gk [ticket:13313#comment:24 observed] that different operating systems render glyphs in the same font differently:

I just tested that on two 32bit Linux systems (one Ubuntu 12.04 and one Debian testing) and even there are differeces visible with bundled fonts (the diff is attached). I guess this means shipping the alpha with it is fine (it can't get worse wrt to the status quo :) ) but we might want to have an estimation about what the current solution really helps us for the stable series before we ship it there.

So I wonder whether it's possible to force Firefox/Tor Browser to use a cross-platform method for rendering fonts.