I have the same problem described here whereby on higher dpi displays, firefox appears to be scaling my whole site up by 20%. This includes all site elements, not just text.
Is there a way to force firefox to display pixel-pixel accuracy? for example, I have a wrapper set to 800px at wider viewports, however, firefox is ignoring this by increasing it by 20%, which causes scrolling. a working copy of the site is here
I have already set viewport and css reset.
The same issue is described here Note that don't want a local fix for this, but something that will work for anyone that views the site.
Thanks.