Does this happen on other web browsers as well (such as Safari). It could be that a font file on your operating system is damaged.

However, it's likely just a Firefox setting. Go to the Firefox settings and check the Fonts & Colors section. Click the Advanced button and make sure that the Allow pages to choose their own fonts, instead of your selections above option is checked. Double check the additional font settings to make sure that the rest of the settings are ok.

I've attached an image of my font settings (I believe that I've kept mine as default) to give you a rough idea of the standard settings.

If that doesn't help, try Firefox Safe Mode to see if the issue goes away. If it's not present in safe mode, the issue is likely caused by an extension installed on Firefox.

Hope this helps.

Would you please try this :

Type in the address bar about:config (press Enter) (promise to be careful, if asked)

Type in the address bar and look for the preference :

security.sandbox.content.level and set its value to 2 (default value is 5 )

Then close and restart Firefox in order for the change to take effect.

Does that make a difference  ?

If not : try a value of '1' (or another value)

If none of the other values make a difference, set it back to its default (and don't forget to close and restart Firefox)

Changing the value to 2 should do the trick though ......

It does not do this in any other browser and changing the sandbox did nothing and I had tried that before. I really like FireFox but need a fix or will need to switch.

Note that on Mac the default is 3. You probably need to set security.sandbox.content.level to 1 to lower the sandbox security and allow access to specific folders.

You may have to whitelist specific font locations if you use an external font manager.

See also:

• https://wiki.mozilla.org/Security/Sandbox#Content_Levels

cor-el said

Note that on Mac the default is 3.

Thank you for pointing that out.

You probably need to set security.sandbox.content.level to 1

That was my second suggestion - unfortunately none of them do the trick

Thanks for the input, guess a new browser is in my future.

What font is Firefox trying to use instead of the font that is specified?

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

You can check the font used for selected text in the Font tab in the right pane of the Inspector. Note that this is not about the font-family CSS rule, but about the font that Firefox actually uses as shown in the Font tab. See also:

• https://developer.mozilla.org/en/Tools/Page_Inspector/How_to/View_fonts

Verdona

Verdana?

One other thing you could try while you wait for any authoritative explanation is to try a fresh Firefox profile.

New Profile Test

This takes about 3 minutes, plus the time to test some affected sites.

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Click the Create a New Profile button, then click Next. Assign a name like July2018, ignore the option to relocate the profile folder, and click the Finish button.

After creating the profile, scroll down to it and click the Set as default profile button below that profile, then scroll back up and click the Restart normally button. (There are some other buttons, but please ignore them.)

Firefox should exit and then start up using the new profile, which will just look brand new. Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test.

Do problem sites work any better in the new profile, or does the same problem recur?

When you are done with the experiment, open the about:profiles page again, click the Set as default profile button for your normal profile, then click the Restart normally button to get back to it.

You can check in Font Book for font issues like corrupted and duplicate fonts.

• https://appletoolbox.com/2016/07/fix-corrupt-user-accounts-macos/
• OnyX
  https://www.titanium-software.fr/en/onyx.html

Wesley Branton said

Does this happen on other web browsers as well (such as Safari). It could be that a font file on your operating system is damaged. However, it's likely just a Firefox setting. Go to the Firefox settings and check the Fonts & Colors section. Click the Advanced button and make sure that the Allow pages to choose their own fonts, instead of your selections above option is checked. Double check the additional font settings to make sure that the rest of the settings are ok. I've attached an image of my font settings (I believe that I've kept mine as default) to give you a rough idea of the standard settings. If that doesn't help, try Firefox Safe Mode to see if the issue goes away. If it's not present in safe mode, the issue is likely caused by an extension installed on Firefox. Hope this helps.

Tried both of these and neither worked.