After updating Firefox to 159.0, two Firefox windows were opened again!

Hi, I'm a little suspicious that one of your add-ons could be involved.

Tips for checking those: Review installed extensions

If you launch a new window using Ctrl+N, does the Yahoo search page appear? That would indicate that it was set as your home page. To edit that, see: How to set the home page.

If it only appears when you use your Firefox desktop/taskbar shortcut, the shortcut might be "hacked." We can describe how to clean that up if you see a connection there.

Did you find anything so far?

The issue only occurs sometimes when Firefox is updated. I found out the Yahoo search page is set as my Home page.

Thank you for the additional info.

It's normal to get a "What's new" page AND your home page (or previous session restored) after an update, so if you saw that combination, it's normal.

I don't think anyone would intentionally choose that particular Yahoo address as their home page. You could simplify it to just https://www.yahoo.com/ if you prefer Yahoo as your home page.

It should not be normal that when the only one Firefox Window that was open is closed, when it restarts, two Firefox Windows automatically open.

If it wasn't the "What's New" page, which usually is an added tab in your main window, I agree you shouldn't get an unexpected page. That sounds suspicious, which was one reason for suggesting an extension check.

How do I check my Extensions? The issue I described only happens sometimes though when I update Firefox. It would seem like the Extensions I have wouldn't have any effect on what Firefox does when it starts. See screenshot of my Extensions.

The ones with the trophy cup are in a select group that gets human review in addition to automated review, so I'm not suspicious of those. The others look fairly standard/popular, so unless their recent reviews report bad behavior, I think those are probably fine.

To clarify the pattern, does this occur when you are restarting Firefox from inside an existing session (either there's a notice or Firefox won't let you load any more pages until you update), or when Firefox updates at startup from a desktop/Taskbar icon?

If the desktop/Taskbar icon is involved, you can check whether it specifies loading any pages at startup:

• right-click > Properties (on the Taskbar, you might need to right-click the pinned shortcut, then right-click Firefox and then right-click Properties)
• Windows should select the Shortcut tab but, if it doesn't switch to the Shortcut tab
• Check the Target line to see whether it has any parameters after the standard command
  "C:\Program Files\Mozilla Firefox\firefox.exe"

I tried closing and restarting Firefox five times from the Firefox Taskbar icon using Windows 11. It always opened only one Firefox Window. The first two times, the only additional Tab that was added was a Firefox info thing. The third time I started Firefox a Firefox Info Tab was added plus a Yahoo Search Tab. After the next two restarts, only a Yahoo Tab was added, as I recall.

I believe the only time a second Firefox Window is opened with a Yahoo Search Tab is when restarting the computer with Firefox running for a Windows 11 Update.

As for trying to follow your check to see what is specified upon Startup, I do not get the Properties option you mention.