Can you clarify what you want to achieve ?

Is this about opening a new window or about switching between existing Firefox windows or something different ?

See also:

• https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly
• https://support.mozilla.org/en-US/kb/mouse-shortcuts-perform-common-tasks

next window, not next tab. i have two windows open, one for pocket and other junk, and the other one what i am doing. so i go to the firefox logo in upper left and figure out which is the one i want to go to. it should be something like control right arrow or such, but it is not on those lists.

You can try "Alt + ~" like works on Mac to switch windows of the current application. Hold Shift in addition to go to the previous Firefox window.