Cntl-shft-t restores previous sessions but if you close before restoring previous sessions they will be gone. And ifnit didn't crash when closing it should show up in the history listing.

Currently, I only show one tab in each window in Firefox. How do I get back the + sign to have additional tabs in the same window?

Hey,

You can attempt to re-attach your New Tab button using the Customise tool provided by Firefox. From the top right (click the two arrows facing right if they're available for a shortcut), hit the menu button (☰) --> Customise Toolbar (sometimes through More Tools >). Find the "New Tab" item and throw it at the end of your toolbar to get it back. If you can't find it, hit "Restore Defaults" at the bottom right.

In the event this does not work, try Ctrl + T to check if the functionality is still there. It is possible that a bug or extension you own is conflating with your ability to open tabs, try opening Firefox in Troubleshoot mode (Menu button (☰) > Help > Troubleshoot Mode) to see if the issue persists.

Cheers,

I do not have a "new Tab" in More Tools. Ctrl + T does nothing. I tried the Troubleshoot Mode and it is no long in the Customise Toolbar, but do not know what to do with it? My Firefox version is 137.0 (64-bit). What would be your next suggestion?