When you say two processes, do you mean the Task Manager (Ctrl+Shift+Esc) Processes tab lists firefox.exe twice, or there is one Windows process with two separate windows, which is the more normal situation?

Another way to tell whether two Firefox windows are in the same process is to open a regular non-private window from one existing window (for example, Shift+click a link or bookmark), and then close it. Does it appear on the History menu in both remaining windows as a window you could re-open?

Even if there is only one process, it's still not normal to get two windows if you didn't double-click and do not have multiple home pages. Sometimes desktop shortcuts are hijacked by software adding URLs to the target path, but that usually would be to an unwanted page, not your normal home page.

Is it possible that Firefox is restoring your previous session windows and tabs in some broken way? Normally, if Firefox has restored your previous session, the "Restore Previous Session" entry on the History menu will be grayed out. Of course, it also will be grayed out if you set Firefox to clear browsing history at shutdown, so it's not a definitive sign. However, if Restore Previous Session is not grayed out, then we can assume that it is not a session restore problem.

Do you use any sandboxing software that might not be integrating correctly with Firefox, resulting in one "unprotected" window/process and one sandboxed window/process?

> When you say two processes, do you mean the Task Manager > (Ctrl+Shift+Esc) Processes tab lists firefox.exe twice, or there is one > Windows process with two separate windows, which is the more > normal situation?

Task manager shows one process. Task manager shows two applications.

> Another way to tell whether two Firefox windows are in the same > process is to open a regular non-private window from one existing > window (for example, Shift+click a link or bookmark), and then close it. > Does it appear on the History menu in both remaining windows as a > window you could re-open?

I have absolutely no idea what you are saying. :D I have "Use customs settings for privacy" and "Always use private browsing mode" enabled.

> Sometimes desktop shortcuts are hijacked by software adding URLs to > the target path, but that usually would be to an unwanted page, not > your normal home page.

They are perfectly fine.

> Is it possible that Firefox is restoring your previous session windows > and tabs in some broken way? Normally, if Firefox has restored your > previous session, the "Restore Previous Session" entry on the History > menu will be grayed out. Of course, it also will be grayed out if you set > Firefox to clear browsing history at shutdown, so it's not a definitive > sign. However, if Restore Previous Session is not grayed out, then we > can assume that it is not a session restore problem.

Nothing there either.

> Do you use any sandboxing software that might not be integrating > correctly with Firefox, resulting in one "unprotected" window/process > and one sandboxed window/process?

EMET. Turning it off didnt solve the problem.

BUT THE PROBLEM WENT AWAY after I set "Never remember history" and (then, since its invisible otherwise) "Clear all current history" (and put it again to "Use custom settings for privacy") and restarted the Firefox. APPARENTLY there WAS some strange session lurking somewhere or some corrupt cache or something that causes this. This is strange, since there shouldnt be any cache/session/history in Firefox with those settings AND I have used software such as CCleaner and Privazer to wipe all history files from Firefox anyway.