I can't reproduce this. Does it still happen in Troubleshoot Mode?

You can check that those pages aren't set as multiple homepages.

You can check the homepage setting in "Settings -> Home".

• https://support.mozilla.org/en-US/kb/how-to-set-the-home-page

Firefox supports multiple homepages separated by '|' (pipe) symbols.

UPDATE: Now it's happening even when I shut down the computer. After I start up my computer, I open Firefox in an incognito window. But when I open a regular window, it reopens the lone tab that was open from when I shut down everything.

Again, "Open previous windows and tabs" is unchecked.

The last session will be restored if the browser crashes or is left open while shutting down Windows. You can disable this by changing browser.sessionstore.resume_from_crash and toolkit.winRegisterApplicationRestart to false in about:config.

You can possibly set browser.tabs.closeWindowWithLastTab to false in about:config to make is possibly to close Firefox with no tab opened.

I am also having this issue on Firefox 124.0.1 on Windows 11. I ensured "Open previous windows and tabs" was unchecked and was also able to replicate the issue in Troubleshoot Mode.

I also tried changing both "browser.sessionstore.resume_from_crash" and "toolkit.winRegisterApplicationRestart" to false without success.

Additionally, I have noticed that even if Firefox is closed completely, if a new incognito window is opened first (e.g. by right-clicking the icon and selecting "New private window"), opening a new regular window (that's not private) will restore previously closed tabs from the last session. However, if a regular window is opened first, tabs are not restored.