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

[Jeff King]

Package: firefox
Version: 49.0-5
Severity: normal

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.

This is the case even when run in --safe-mode; the dialog asking to
confirm running in safe-mode has small fonts and buttons.

Setting GDK_SCALE=2 improves the situation, but my understanding is that
this is supposed to happen automatically. This seems to be a gtk3 thing,
as installing gtk-3-examples and running gtk3-demo shows the same
problem. So I doubt there's a particular bug to fix on the _firefox_
side, but it is a potential data point against enabling gtk3 (i.e., from
my perspective it's a regression in firefox).

-- Package-specific info:

-- Extensions information
Name: BugMeNot Plugin
Location: ${PROFILE_EXTENSIONS}/{987311C6-B504-4aa2-90BF-60CC49808D42}.xpi
Status: enabled

Name: Dactyl Binary Utils
Location: ${PROFILE_EXTENSIONS}/binary
Status: user-disabled

Name: Default theme
Location: /usr/lib/firefox/browser/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}.xpi
Package: firefox
Status: enabled

Name: Google Redirects Fixer
Location: ${PROFILE_EXTENSIONS}/jid1-zUrvDCat3xoDSQ at jetpack.xpi
Status: enabled

Name: HTTPS Everywhere
Location: ${PROFILE_EXTENSIONS}/https-everywhere at eff.org.xpi
Status: enabled

Name: Multi-process staged rollout
Location: ${PROFILE_EXTENSIONS}/e10srollout at mozilla.org.xpi
Status: enabled

Name: PassFF
Location: ${PROFILE_EXTENSIONS}/passff at invicem.pro.xpi
Status: enabled

Name: Pentadactyl
Location: ${PROFILE_EXTENSIONS}/pentadactyl at dactyl.googlecode.com.xpi
Status: enabled

Name: Pocket
Location: ${PROFILE_EXTENSIONS}/firefox at getpocket.com.xpi
Status: user-disabled

Name: uBlock Origin
Location: ${PROFILE_EXTENSIONS}/uBlock0 at raymondhill.net.xpi
Status: enabled

Name: uMatrix
Location: ${PROFILE_EXTENSIONS}/uMatrix at raymondhill.net.xpi
Status: enabled

Name: Web Compat
Location: ${PROFILE_EXTENSIONS}/webcompat at mozilla.org.xpi
Status: enabled

-- Plugins information
Name: Shockwave Flash (11.2.202.643)
Location: /usr/lib/flashplayer-mozilla/libflashplayer.so
Package: flashplayer-mozilla
Status: enabled


-- Addons package information
ii  firefox        49.0-5       amd64        Mozilla Firefox web browser
ii  flashplayer-mo 3:11.2.202.6 amd64        Macromedia Flash Player

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.7.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)

Versions of packages firefox depends on:
ii  debianutils               4.8
ii  fontconfig                2.11.0-6.7
ii  libasound2                1.1.2-1
ii  libatk1.0-0               2.22.0-1
ii  libc6                     2.24-5
ii  libcairo-gobject2         1.14.6-1+b1
ii  libcairo2                 1.14.6-1+b1
ii  libdbus-1-3               1.10.12-1
ii  libdbus-glib-1-2          0.108-1
ii  libevent-2.0-5            2.0.21-stable-2.1
ii  libffi6                   3.2.1-6
ii  libfontconfig1            2.11.0-6.7
ii  libfreetype6              2.6.3-3+b1
ii  libgcc1                   1:6.2.0-10
ii  libgdk-pixbuf2.0-0        2.36.0-1
ii  libglib2.0-0              2.50.1-1
ii  libgtk-3-0                3.22.2-1
ii  libgtk2.0-0               2.24.31-1
ii  libhunspell-1.4-0         1.4.1-2+b1
ii  libnspr4                  2:4.12-6
ii  libnss3                   2:3.26.2-1
ii  libpango-1.0-0            1.40.3-3
ii  libsqlite3-0              3.15.0-1
ii  libstartup-notification0  0.12-4
ii  libstdc++6                6.2.0-10
ii  libvpx4                   1.6.0-2
ii  libx11-6                  2:1.6.3-1
ii  libxcomposite1            1:0.4.4-1
ii  libxdamage1               1:1.1.4-2+b1
ii  libxext6                  2:1.3.3-1
ii  libxfixes3                1:5.0.2-1
ii  libxrender1               1:0.9.9-2
ii  libxt6                    1:1.1.5-1
ii  procps                    2:3.3.12-2
ii  zlib1g                    1:1.2.8.dfsg-2+b3

firefox recommends no packages.

Versions of packages firefox suggests:
pn  fonts-lmodern          <none>
pn  fonts-stix | otf-stix  <none>
pn  libcanberra0           <none>
pn  libgnomeui-0           <none>
ii  libgssapi-krb5-2       1.15~beta1-1
pn  mozplugger             <none>

-- no debconf information