Did you try to close (Quit) and restart Firefox? Did you try to open a new window and close this window?

Sorry if these are obvious questions, but just in case:

• Does the Window menu shows that the missing tabs are in a different window?
• Can you cycle among open tabs in the current window using Command+Tab?
• Are you using any custom style rules (userChrome.css) to change the appearance or position of the tab bar?

Note for userChrome.css users: Some time back there was a change in Firefox and some old rules piled all the tabs on top of one another in a weird location on screen. If you just recently switched from the Extended Support Release of Firefox 102 to the Extended Support Release of Firefox 115, your old style rules may need a bunch of updates to work with the later version.

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 System 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