Hi there, I understand that when you restart Firefox that there are only 3 windows that restore, despite Tab Mix Plus being disabled in your Firefox profile. I am happy to help.

From my experience with that add-on, there are a number of about:config entries that are customized from the preferences that are set within the extension's settings. There is a way to check if any of those added entries are still controlling the # of windows that are restoring. Can you please go to about:support, click on "I understand the risks" and take a screenshot of the entries that show up when you search for "mix" and then another when you search for 'session'?

I am looking to see if there are any bold, or added configs that may still be active even though the browser has disabled the add-on.

Another troubleshooting method that might also be easier is uninstall Tab Mix Plus from the profile. Would that be an option?

Hi hanspeter123, in case this is not a problem with leftover settings from Tab Mix Plus, here are the next things to consider:

Can you recover additional windows from the menu?

When a session has been restored, up to three previously closed windows may available on either:

• "Library" toolbar button > History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)
• (menu bar) History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)

Does that help, or were you using that already?

What method do you use to exit out of Firefox?

If you use the menu, either --

• "3-bar" menu button > Exit
• (menu bar) File > Exit

-- then all the windows you have open when you execute that command should be available to restore, plus the last three windows you had closed before that.

But! If you use a method that closes individual windows, whether you do that by hand or let Windows do it, then you will lose windows. By default, Firefox only retains the last three closed windows in session history, so those are the only ones that will be available to restore.

So my recommendation is, always exit out of Firefox using the menu.

However, if you want to keep using a method that closes individual windows, you could modify this setting:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.max_windows_undo preference to display a dialog where you can enter the desired value (for example, I increased mine from 3 to 10), then click OK

Keep in mind that saving more session history does affect performance because Firefox updates the file as often as every 15 seconds.

Hey, thanks alot for your help. The issue wasn't caused by any addon, I was able to recreate it in safe mode, with a completely new profile and with all addons disabled manually. Maybe I should've written that in the first post, sorry.

There weren't any entries in the "Recently Closed Windows" menu, I tried this already (maybe should've specified this aswell. Again, sorry)

I was closing the windows through "right-click taskbar icon -> close all windows" and increasing the "browser.sessionstore.max_windows_undo" setting seems to have solved my problem.

Again, thank you very much - only being able to restore 3 windows was driving me nuts for some time now. I wish I had asked here sooner instead of spending months and months trying to futily fix this myself.

Note that there are also prefs that set the number of item in the back/forward tab history as stored in sessionstore files.

• browser.sessionstore.max_serialize_back = 10
• browser.sessionstore.max_serialize_forward = -1

The default for max_serialize_back is 10. A value of -1 will disable this maximum and allows to keep all back history entries.