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Browser displays hex a in square instead of actual text characters.

  • 6 replies
  • 1 has this problem
  • 483 views
  • Last reply by swampgrafx

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After years of stable operation this behavior began after an OS system update enabled me to update Firefox to 64.0.xx. I've tried both Refresh Firefox, and trashing prefs.js, without success. All social sites affected, Feedly, and others.

Noted: Firefox (preferred browser) is now the application associated with all html, json, js, and perhaps other files.

Attached screenshots

Modified by swampgrafx

Chosen solution

What font is Firefox trying to use?

You can right-click and select "Inspect Element" to open the builtin Inspector with this element selected.

You can check in the Rules tab in the right panel in the Inspector what font-family is used for selected text. You can check in the Font tab in the right panel in the Inspector what font is actually used because Firefox might be using a different font than specified by the website.


You can check for sandbox security issues when Firefox has a problem to access fonts installed locally.

You can set this pref to 2 or 1 on the about:config page to reduce the sandbox security level.

  • security.sandbox.content.level = 1
  • close and restart Firefox to make the change effective.

If '1' still doesn't have effect then try '0' to disable the sandbox.

If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value.

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

See also:

Read this answer in context 👍 0

All Replies (6)

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Type about:preferences#content<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own.

Fonts Information - Detected via Flash http://browserspy.dk/fonts-flash.php?detail=1

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Chosen Solution

What font is Firefox trying to use?

You can right-click and select "Inspect Element" to open the builtin Inspector with this element selected.

You can check in the Rules tab in the right panel in the Inspector what font-family is used for selected text. You can check in the Font tab in the right panel in the Inspector what font is actually used because Firefox might be using a different font than specified by the website.


You can check for sandbox security issues when Firefox has a problem to access fonts installed locally.

You can set this pref to 2 or 1 on the about:config page to reduce the sandbox security level.

  • security.sandbox.content.level = 1
  • close and restart Firefox to make the change effective.

If '1' still doesn't have effect then try '0' to disable the sandbox.

If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value.

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

See also:

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FredMcD said

Type about:preferences#content<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own. Fonts Information - Detected via Flash http://browserspy.dk/fonts-flash.php?detail=1

Tried this first, no effect.

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cor-el said

What font is Firefox trying to use? You can right-click and select "Inspect Element" to open the builtin Inspector with this element selected. You can check in the Rules tab in the right panel in the Inspector what font-family is used for selected text. You can check in the Font tab in the right panel in the Inspector what font is actually used because Firefox might be using a different font than specified by the website.

You can check for sandbox security issues when Firefox has a problem to access fonts installed locally.

You can set this pref to 2 or 1 on the about:config page to reduce the sandbox security level.

  • security.sandbox.content.level = 1
  • close and restart Firefox to make the change effective.

If '1' still doesn't have effect then try '0' to disable the sandbox.

If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value.

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

See also:

level 3 > 1; two more parameters show as modified. Fixed! Thank you.

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Do you know what font Firefox couldn't access and that made Firefox fallback to a last resort font ('A')?

The Font tab in the Inspector should show this. This usually happens when Fonts are installed by third-party font managers.

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cor-el said

Do you know what font Firefox couldn't access and that made Firefox fallback to a last resort font ('A')? The Font tab in the Inspector should show this. This usually happens when Fonts are installed by third-party font managers.

Helvetica Neue, which seems strange because that's pretty much universal. It looked like it might have broken the CSS. I use FontExplorer Pro and it may have coincided with the first time I launched the app after system update - I have two versions of Hel Neue, should probably prune.