It looks like maybe the problem is Firefox since it seems to be ok when I access the site through Google Chrome.  Is Firefox incompatible?  I’ve been using Box and Firefox for years and have never before had this problem (although I typically access my documents through the synched folder on my desktop.

Hi ​@Michael Black  Welcome to the Box Community!
 

If you're able to view your documents in a browser like Chrome but not in Firefox, it may be an issue with the browser itself. Box supports the two most recent major versions of Firefox. Versions older than two major releases, including Extended Support Release (ESR) versions, are not supported. If you're encountering interface issues, we recommend updating your browser (or OS) to the latest version if you haven't already.
 

For more details, check out this support article: Understand the Box Policy For Browser And OS Support
 

Additionally, clearing your browser’s cache and cookies often resolves browser-related issues. If the problem persists, you may need to submit a support ticket so our Product Support team can investigate the issue further, especially regarding blacked-out documents.

We hope this helps! Have a great day!