I should add that I have my bookmarks always displayed as sidebar on left of screen. The info is hidden under that. I know this because when I remove the sidebar, I see the missing column. This was not a problem on the Windows 10 laptop I was using. Any thoughts?

I see the left panel and I don't use the sidebar. You can move the sidebar to the right but then it will cover your chat list.

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I tried the sidebar on the newsfeed in FB this morning. The FB columns moved to the right and contracted so I was still able to see all of them. Do you have any extensions which could be causing the problem?

What extensions should I check?

See the links posted by cor-el.

I tried but cannot find what cor-el is saying I need to change. :/

Does the problem persist if you start Firefox in troubleshoot mode?

I'm a bit of a rookie when it comes to this type of troubleshooting. I greatly appreciate everyone trying to help. I just need it put in plain English, if possible.

Use either menu > Help > Troubleshoot Mode.

Tried Troubleshoot mode...Bookmarks sidebar is still covering the far left column of FB. I cannot find "3-bar" menu button spoken of above. :/ I guess my wife will have to use Chrome for FB (everything works fine there although she cannot have her Bookmarks on the side) and use Firefox for everything else.

Check this section of the support article.

https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_the-problem-happens-in-troubleshoot-mode