Profile data can be removed or not recorded in several ways;

• 1) Running Firefox in Private Mode (nothing is recorded)

That's what I would expect, but obviously in my case it works inversely: When reopening Firefox, I always get the tabs of the last closed window, even if it was private. What I want when I open Firefox (and what I got before one of the latest updates, if I remember correctly) are the tabs of the last non-private window.

Hmm, I don't think private window tabs should ever be restored, so that is very troubling. The restored window has the white-mask-on-purple-circle at the upper right?

Can you recover the closed regular window using either:

• "3-bar" menu button > Library > History > Recently Closed Windows
• "Library" toolbar button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows

Thank you! The Answer to your question: The restored window is NOT private.

PS: Yes, I can recover the regular tabs as described.

I was sure I could (and did) reproduce the error before I opened this problem, but now I can't :-(. Maybe I unintentionally opened multiple regular windows and mixed it up with my private window (normally one), so that the last window closed was indeed a regular one. So I will mark this as solved until I get the "error" again.

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have Private Browsing mode windows open.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

Note that this can happen if you first close the regular window and then close the PB mode window. That makes Firefox think you close a PB mode session and sessionstore.jsonlz4 isn't created.

Yes, that describes excactly my problem! But is there a setting to prevent this, i. e. making Firefox to remember always the last closed regular window?

First, you need to be careful about what window gets closed.

Sometimes when surfing, I end up accidentally closing the window. A bit of a hassle getting it back but I found a better way. When I start the browser, I drop the first window to the taskbar. I then open a second window and do my work in it. Now if I happen to close the work window, I use the first window to call it back.