Bug#843104: firefox: gtk3 makes fonts tiny on hi-dpi display

[Jeff King]

On Thu, Nov 03, 2016 at 04:31:54PM -0400, Jeff King wrote:

> Since the move to GTK3 in 49.0-5, the fonts and widgets on my hi-dpi
> (3840x2160, 240dpi) display are tiny. The actual rendered content is
> sized as it was with GTK2.

A few other data points:

 - the rendered content is sized appropriately with GTK3 only because
   I had previously set layout.css.devPixelsPerPx to "2". Setting it
   back to the default of "-1.0" makes the rendered content small with
   GTK3.

 - Setting the font size in .config/gtk-3.0/settings.ini like:

     [Settings]
     gtk-font-name=Sans 24

   helps quite a bit, but is just working around the issue (the
   resulting size is closer to what "Sans 10" looks like in an XTerm,
   not 24pt).

 - Using a large font _without_ setting devPixelsPerPx looks quite bad,
   as the tab titles do not fit inside the tabs themselves.

So I _think_ the root cause of all of this is that GTK3 for whatever
reason is not getting an accurate DPI for my system. Possibly because
I'm not running GNOME or any modern desktop environment (I'm using
AwesomeWM, FWIW).

With the two tweaks (an oversized font setting, and devPixelsPerPx)
things seem usable, but those really feel like workarounds.

-Peff