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Letters on many websites display as letter A in a box - this just strated today - how can I fix?

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  • Last reply by cor-el

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Text on websites displays as letter 'A' in boxes. Restart does not fix. Is there a preference I can adjust, or a font configuration that has changed?

Text on websites displays as letter 'A' in boxes. Restart does not fix. Is there a preference I can adjust, or a font configuration that has changed?
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Chosen solution

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

  • 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.

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This can happen when Firefox has a problem to access locally installed fonts because of sandbox security issues. https://wiki.mozilla.org/Security/Sandbox


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.

[v56+] Type about:preferences#general<enter> in the address bar. Under fonts and colors, press the Advanced button. Scroll to 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

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

  • 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.