How to cycle through Firefox tabs "normally"?

I reinstalled Firefox, version 63, and now Ctrl+Tab and Ctrl+Shift+Tab don't work to cycle through existing tabs. If I open Firefox and open a second tab, Ctrl+Shift+Tab does nothing, and I expected it to return to the first tab. If I hold the Ctrl+Tab keys, I have a thumbnail preview of Firefox tabs, as in this picture:

How can I get the "normal" behavior?

Solution 1:

That sounds like Ctrl+Tab is using the recently used order.  You can change settings by going to the “Options” page by one of the following procedures:

• type “about:preferences” into the address bar
• click on the “hamburger” (≣) and select “Options” from the menu
• select “Options” from the “Tools” menu

and then, in “General” → “Tabs”, uncheck “Ctrl+Tab cycles through tabs in recently user order”.