Can you provide a link to a page demonstrating this problem?

When I look up CJK it appears there are potentially many variables in what fonts Firefox might use: https://en.wikipedia.org/wiki/CJK_characters

you can visit baidu.com and search for anything. On the result page, you will find the boxes. Right click and inspect element, find don't weight: bold and check it off and the characters are back

Thanks, I don't have Firefox 57 on this computer, but I viewed the Baidu results page in Firefox 59 ("Nightly" test version). On my Windows 7, the Meiryo Bold font is used. (Screenshot attached.)

Can you check what font is used on yours? In the Inspector, switch from the Rules panel to the Fonts panel. If the heading is not visible, try the little triangle at the end of that row of headings.

Thank you for your feedback. I tried the same page got the same problem in Firefox 58. But now I have a better understanding of the problem. The webpage sets Arial as the font-family and whenever font-weight goes beyond 600 or set to bold, the browser will use Arial Black as the font and caused the boxes. I forced user setting of Noto Sans to replace the webpage setting of fonts, and boxes are gone. The same page displays properly in chrome. So I think it is still the brower's problem. It should fallback to the user font setting when it can't handle the font. When font weight is 500 or below, it does. When it goes beyond 600, it doesn't.

It's odd because Firefox should know better than to try to find those characters in Arial Black...

If you check your font settings, do they look like the attached? This is from the English U.S. version.

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Under Language and Appearance, click the "Advanced" button. Then use the selector at the top to check different character sets.

Yes, the default font setting is the same, but it doesn't work properly. I compared with Edge and the same element in Edge will automatically fall back to Yahei no matter what font-weight it has. In Firefox 58, it will fall back to Yahei when font-weight is 500 or below, but when font-weight is 600 or above, it won't fall back and stick with Arial Black.