firefox is acting weird in spaces

i notice recently that firefox does not behave normally in spaces. i assigned this app to space. when i have 3-4 firefox browsers open up in this space, using 'all window' the browsers all line up in oone horizontal instead of scatter all over the screen.

this happens when firefox is the only application in this space. when i have other app in the same space, they look fine using 'all window'.

any other apps behave normally in any spaces, except firefox by itself. i look for the space plist, but i can't find any. i disable and re-enable space, but get the same result with firefox.

anyone has the same experience? any suggestions?