Hi   !

Two things come to mind :

Make sure that you're not in permanent private browsing mode :

3-bar menu (or 'Tool's) => Advanced => Privacy => under 'History'": choose 'Use custom settings for history' and make sure that 'Always use private browsing mode' is unchecked.

And also :

Type in the address bar about:config (press Enter) (promise to be careful, if asked) Type and look for the preference : layout.css.visited_links_enabled and make sure that its value is set to true

Any difference  ?

I checked and do not have private browsing. Visited links are highlighted on the yahoo search page. the about:config was interesting but did not help. My company uses Firefox at work also and I have the same problem there. I think version 53 works but I don't have it for test.

Thanks for your prompt reply. I do appreciate that.

Bummer  ! There might be problems with the places.sqlite database file (bookmarks, history) in the Firefox profile folder.

You could give this add-on a try :

https://addons.mozilla.org/firefox/addon/places-maintenance/

If the Places Maintenance extension can't repair the places.sqlite database file then remove all places.sqlite file(s) in the Firefox profile folder to make Firefox rebuild the places.sqlite database file from the most recent JSON backup in the bookmarkbackups folder. You can check whether the bookmarkbackups folder has a useful backup to ensure that the bookmarks can be rebuild.

http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox

Note that I see the same and if I click a link on that page then I do not see the visited state. I think they use a style sheet to apply the same color to a:link and a:visited. If I disable website colors or apply visited code via userContent.css then I see the visited state.

I apologize fro my ignorance. How do you "apply visited code via userContent.css"?