Your screenshot suggests two different issues:

(1) When you launch one or more private window, Firefox shows a separate button on the Taskbar for the private window(s). Firefox has been doing this for a while.

(2) The private window button has been pinned to the Taskbar, when previously it was on the Start menu and not pinned. You can right-click the button and choose "Unpin from Taskbar" to undo this.

What did you want to change?

Your screenshot suggests two different issues: (1) When you launch one or more private window, Firefox shows a separate button on the Taskbar for the private window(s). Firefox has been doing this for a while. (2) The private window button has been pinned to the Taskbar, when previously it was on the Start menu and not pinned. You can right-click the button and choose "Unpin from Taskbar" to undo this. What did you want to change?

First of all sorry for my poor english.

im talking about (1) when i launch privet window it show differrent button but before it not show,can i set it in same place like before

You can try this:

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

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste browser.privateWindowSeparation.enabled and pause while the list is filtered

(3) Double-click the preference to switch the value from true to false

Probably that will take effect the next time you exit out of Firefox and start it up again.

So normally i can not change it from settings ?

There isn't an option for this on the Settings page.

damn i like previous system new one is not good,they should give an option who wanna use previous one.

Simply change browser.privateWindowSeparation.enabled to false in about:config.