With certain Windows fonts there is a display issue where ligature-kerning seems to flip out and make the two letters bold. Here's a screenshot of an email using Helvetica in Firefox:

enter image description here

As you can see, it seems to be something about the way crossed characters (t and f) connect to each other and letters like i.

I've had this problem for a very long time (over multiple systems) and wondered if anybody has ever seen similar issues popping up and found a way to fix them.

Note: I think this does just affect Firefox. Chrome and LibreOffice are both fine.


Another solution that will work with all applications, including Libre Office, is given by aldeby:

Edit or create the file ~/.fonts.conf and paste this code in it:

<match target="font" >
<edit name="embeddedbitmap" mode="assign">

Make sure to keep the XML structure.

Log out and in again, and Calibri (and possibly some other fonts) will look much better (actually even better than with the other answers given here, because the ugly bitmap substitutions are completely disabled).

  • 3
    This one's a better solution than the earlier ones, as it's a global fix, and eliminating ligatures is a bodge. Ligatures are there to make text more pleasing to read, and to turn them off to work around a configuration problem is not ideal. – scruss May 20 '13 at 13:58
  • Anyone who is slightly OCD or anal retentive enough to care about properly formatting the contents of this XML file (of course you Linux folks would never care about such things ;-) ): <?xml version="1.0"?><!DOCTYPE fontconfig SYSTEM "fonts.dtd"><fontconfig><match target="font"><edit name="embeddedbitmap" mode="assign"><bool>false</bool></edit></match></fontconfig> – Adam Plocher Oct 19 '16 at 1:06
  • Link to aldeby now leads to some phishing scam site – charsi Oct 20 '18 at 15:21
  • 1
    @charsi thanks, I replaced it with a link to the Web Archive. – Calimo Oct 20 '18 at 15:26

Disabling ligatures (see Calimo's fonts.conf answer) is the wrong direction! It may remove those over-aliased "bold" ligatures in fonts like Calibri, but it also removes some of the beauty of typography. That's rather similar to shrinking the font until you can't tell the difference.

I solved this for my system by removing the Calibri font, installing Carlito, which is "metric-compatible with Calibri" and is packaged with "a mapping entry to fontconfig (local.conf)," and refreshing my font cache:

$ rm ~/.fonts/microsoft/CALIBRI*
$ sudo apt install fonts-crosextra-carlito
$ fc-cache

You can then verify that Carlito stands in for Calibri:

$ fc-match Calibri
Carlito-Regular.ttf: "Carlito" "Regular"

Before removing Microsoft's Calibri, I saved a test document in LibreOffice that used Calibri and took a screen shot. After doing that, I quit LibreOffice, opened it again, and then loaded my test document. The "Calibri" font name was italicized to indicate that it was substituted for. I took a screen shot of this substituted version and pasted it below the original:

Calibri tests

The above text is a pair of screen shots of 13pt Calibri, with Microsoft's Calibri above Carlito as matched by fontconfig. There is no bold, no formatting, "pair kerning" enabled, as rendered by LibreOffice

Carlito is quite close to Calibri, ligatures render properly, and it's much prettier overall.

You can do the same with Caladea for Cambria with fonts-crosextra-caladea and you can use Google's Croscore fonts Arimo, Tinos, and Cousine for Arial, Times New Roman, and Courier New with fonts-croscore. Learn more at Debian's Substituting Calibri and Cambria Fonts wiki.

But what about Helvetica?

This question asks about the Helvetica font, which is Apple's preferred sans-serif font. Microsoft preferred Arial before it changed to Calibri. The default Linux mapping varies by distribution, but it's typically either Nimbus Sans L or else Liberation Sans, e.g.

$ fc-match Helvetica
n019003l.pfb: "Nimbus Sans L" "Regular"

If you run that and get Arial, that's a pretty good reason for having the ligature issue described above – Arial is not a great font.

Helvetica has quite the culture surrounding it and I can't find a font that is fully metric-compatible with Helvetica. Arial (and fonts metrically compatible with Arial, including Liberation Sans and its fork, Arimo, have identical character widths (which mean they're "mostly" metric compatible; text will wrap the same way as with Helvetica). Among the free fonts, Liberation Sans and Nimbus Sans seem to have the most similar aesthetics.

There's also IBM Plex, a new font with big money behind it[1][2]. Plex is designed to replace Helvetica (it also has condensed sans as well as serif and monospace fonts) in all of IBM's materials, though it is not at all metric-compatible to Helvetica or other fonts. Font Squirrel has a nice view of samples of the Plex fonts.


lgarzo's answer will work only on websites that have a "noligs" class on the text (most websites don't).

To globally disable ligatures on all websites, add the following line to your userChrome.css:

* { -moz-font-feature-settings: "liga" 0; }

The easiest way to do that is to create a new style with the Stylish extension.

  • +1 for the Stylish suggestion. AFAIR I've quoted Mozilla documentation (since I had expected the OP to be able to transform that as he wished :)) My intention was to include the rule into the page's CSS. (Cannot check the source, though. It seems to be down ATM.) – lgarzo Jul 5 '12 at 18:50
  • That syntax was only valid until Firefox 14, according to stackoverflow.com/a/15161336/4464570, and is now no longer recognized by the browser. I edited your post to update it with the current syntax. – Byte Commander Jan 15 '18 at 11:32

A few remarks popped into my mind while looking at the image:

  • The ligatures seem to be anti-aliased, while the rest of the text is not. Therefore it looks fatter than normal text (although I cannot deny it also looks bold).
  • AFAIK the Helvetica font is a non-standard font, i.e. does not come with default Windows installations. Do you have it installed, or is it a different font?

I think the problem is based on the font not supporting ligatures/kerning correctly.

You can disable ligatures in FF with the CSS rule below:

/* disable common ligatures, usually on by default */
.noligs { -moz-font-feature-settings: "liga" 0; }

Source: CSS Reference:Mozilla Extensions


In addition to Calimo's answer, Archlinux users can find help https://wiki.archlinux.org/index.php/font_configuration - Disable bitmap fonts

It suggested to created a local config file ~/.config/fontconfig/conf.d/20-no-embedded.conf, but I went for a system wide option

sudo touch /etc/fonts/conf.d/20-no-embedded.conf
sudo chmod 777 /etc/fonts/conf.d/20-no-embedded.conf
nano 777 /etc/fonts/conf.d/20-no-embedded.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
  <match target="font">
    <edit name="embeddedbitmap" mode="assign">

Then just restart the app (in my case thunderbird)

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