Mozilla DPI-related Font Size Issues on Unix
Mozilla Fonts Overview
A number of factors can cause fonts in Mozilla to seem wrong. For web page text, you can choose your default sizes and styles via the UI preferences panel. Typically, web page authors override some or all of your preferences via stylesheets and/or presentational markup. Mozilla has a minimum text size preference and text zoom to help you combat author styles that override your defaults. It is also possible to override author overrides via user stylesheets.
Fonts can seem wrong in Mozilla's menus, tools and bookmarks too. Doing something about it is the topic of this page.
How UI Fonts in Mozilla are Configured
Mozilla sets
UI fonts
by querying the operating system's font subsystem for
CSS system fonts.
In most environments, these are set in
points.
Point sized controls only display at the intended size if the system
DPI is reasonably
configured.
Since some web page authors size text in points, inappropriately
configured DPI also can adversely impact web page text sizes.
DPI Problem Solving
Both points and DPI either too small or too big are
typically caused by a mismatch between your real display size and
the display size your X server thinks you have. So, if you don't like
Mozilla's UI font sizes, start to correct your problem by reconciling
the two sizes. Measure your display, and change whatever settings are
required to cause the X server to report and use the actual display size.
GTK1
Mozilla does not respond to DPI adjustments with corresponding changes in
UI fonts. Adjustments to GTK1 UI fonts must be made
via gnomecc or
via userChrome.css.
To find out what your X server thinks your DPI settings
are, run the program xdpyinfo:
$ xdpyinfo | grep dimensions $ xdpyinfo | grep resolution
Note the dimensions in pixels and millimeters, and the resolution in
DPI. Compare to what you're actually using, but don't
confuse dots and pixels - a dot may or may not equal a pixel. If you have
KDE, kinfocenter's X-Server section will
conveniently show the same information.
For example, if you use a 17" CRT display, your viewable screen dimensions will be approximately 328 mm wide by 246 mm tall. This actual size could traditionally be forced by adding:
DisplaySize 328 246to
Section "Monitor"
in /etc/X11/XF86Config or
/etc/X11/xorg.conf, as
applicable on your system. If you are running a 1400 X 1050
resolution with a 328 mm X 246 mm display, your system will
be running at an actual 108 DPI. This change may
be sufficient to correct your problem. If it fails and you are running
Xorg 7.2 or newer, you may need to add:
Option "NoDDC"to
Section "Device"
for your graphics adapter in order for DisplaySize to work.
If the above change improves your system, but the result is less than 100%
to your satisfaction, you can tweak sizes up or down by making the
DisplaySize dimensions slightly larger or smaller than actual.
Unfortunately, variations in the implementations of X mean display size
reconciliation as above won't be a solution on every system. Failure here
seems to be common on newer systems using
fontconfig instead
of legacy xfs.
Systems using fontconfig provide an option for X and applications that
understand it to set DPI via the Xft.dpi variable.
To find out if Xft.dpi has already been set, check by running
the program xrdb -query:
$ xrdb -query | grep dpi
The regular file
/etc/X11/Xresources is one place this might be set,
where you might find it present, but commented out. On systems with the directory
/etc/X11/Xresources, Xft.dpi can be
set in ~/.Xresources. Another location it can be set is
~/.Xdefaults. On such systems, adding to the applicable file:
Xft.dpi: 108
or uncommenting an existing line would produce the same result as setting
DisplaySize produces for xfs.
On some systems, setting DisplaySize
first, and then setting Xft.dpi to match the reported
DPI is required for proper results.
As above, if this works, but at less than 100% satisfaction, tweak the number lower or higher to suit your preference. If possible, use a number that is a multiple of 6, or even 12, as numbers that aren't sometimes result in annoying rounding errors that cause adjacent bitmap font sizes to not increment and decrement linearly.
All Mozilla.org builds of Firefox and SeaMonkey, some of Mozilla, and
most builds of these products supplied by recent Linux distros, are built
using the GTK2 toolkit. This
means that gnome-control-center can be used
to explicitly set DPI to a desired value that these builds will share with
all other GTK2 apps.
Some users have found success in adjusting the X server's
DPI by doing one of the following:
-
Using the graphical login screen:
In
/etc/X11/xdm/Xservers, change::0 local /usr/X11R6/bin/X
to:
:0 local /usr/X11R6/bin/X -dpi 100
You need to restart xdm for this to work:
$ su - root # telinit 3 # telinit 5
-
Using Redhat and gdm:
In
/etc/X11/gdm/gdm.conf, change:0=/usr/bin/X11/X
to:
0=/usr/bin/X11/X -dpi 100
You will need to restart gdm for this to work
-
In some Debian variants:
In
/etc/init.d/xsession, or/etc/kde3/kdm/Xservers, change:DPI="-dpi 75"
to include whatever DPI you wish to use instead of 75.
You will need to restart X for this to work
-
Using startx from the command line:
$ startx -- -dpi 100
If none of the above or variations thereof work, as a last resort, you
can use the brute force method of forcing Mozilla to use a particular
DPI directly. Edit your user.js file and add:
user_pref("layout.css.dpi", 108);
You may change the DPI number to any resolution you
like. Setting it to 0 will restore Mozilla's use of the X Server
DPI. Like prefs.js, user.js is a plain text file in your
profile directory. If it doesn't exist, create it with your choice of
text editor.
As an alternative to editing user.js, you can change
layout.css.dpi by entering
about:config
in the urlbar, right clicking the current value, and changing it to any number you like.
A third way to change Mozilla DPI by brute force in older
versions is via the preferences UI:
Appearance -> Fonts -> Display resolution
Changes to layout.css.dpi
by any of the three methods above require a complete Mozilla restart
to take effect.
Note that for cross-platform uniformity reasons, Mozilla by
default uses the greater of your system setting or 96. If you wish
Mozilla to use a DPI of less than 96, you must force it
to do so using layout.css.dpi, either automatically by supplying
the parameter 0, or by the DPI integer value you wish used.
Choosing Your Mozilla
Not all Mozilla builds are suitable for all systems. Legacy systems
use the xfs font service system exclusively. Standard
builds must be used on these systems for reasonable results. Newer
systems use the fontconfig font service system in
addition to xfs. You can use any Mozilla build on these
systems, but xft labeled builds should produce clearly
better results.
To find out which type of Mozilla build you are using, enter into the urlbar:
about:buildconfig
Only builds intended for fontconfig systems will
show --enable-xft as a configure argument.
Customizing Fonts Via CSS
Finally, if you still can't get Mozilla's fonts just the way you
like them by changing DPI, you can customize them
directly using standard
CSS 2.1, in
userChrome.css for the UI, and userContent.css
for web page text. How to do this is covered generally at
Customizing Mozilla.
Using CSS, you can customize Mozilla fonts via methods that don't
depend on DPI. A few of the many possible UI CSS
selectors you might wish to try in userChrome.css include:
- menu, menuitem (main menu items)
- statusbar
- .tabbrowser-tabs .tab-text
- toolbar (urlbar)
- .toolbarbutton-1 (nav button text in Modern theme)
- treechildren (mailnews folder & header panes; pref trees)
- .treecol-text (mailnews column headings)
Using DOM Inspector you can explore Mozilla's
application of CSS and find other selectors you might wish to
experiment with.
Help
Forums available for further help with Unix DPI
and fonts include:
- Mozilla newsgroups
- Moznet on IRC