On Corel's home page, their standard fonts are listed for me -- a Windows user -- as:

font-family: "Segoe UI", -apple-system, BlinkMacSystemFont, sans-serif;

Assuming yours are the same, either one of those is messed up or is not compatible with Firefox.

To get a better idea of what is going on, can you give examples of others sites with this problem?

Due to the link spam filter, your reply will be delayed until a moderator can approve it, so if you include URLs and you don't see your post right away, that's normal.

Thanks for your feedback. Here is another example. One screen shot from FireFox and one from Chrome. Perhaps it is a font issue as you suggest but it seems so random.

I can't tell what page that is. To explore what font is being used, you can use Firefox's Page Inspector tool. Here's how:

right-click (or with one button, Ctrl+click) a paragraph that has unreadable text and click Inspect Element

Firefox will open a panel in the lower part of the tab with HTML code on the left and one or two panels on the right. The panels on the right have several different options, the one you want is the Fonts panel.

That panel will show the font the site wants to use, and what font actually is being used. As you browse, keep track of the fonts that aren't working to see whether there is a pattern.

Thanks. I had the same problem with this page http://g.ve00.net/display.cgi?ToyotaMotorSales:1596219035.23819:euniceockerman%40gmail.com&wtID=3k2.1700x.1.3q0w And following your advice I saw that Trebuchet was the font at issue, turned it on and the page corrected itself. Now to look at the Corel site. Your help is much appreciated