That sounds more like a O/S and video driver issue. FF isn't a video driver or O/S driver.

The O/S or video driver did not change. This problem occurred immediately after FF update.

FF cookie is not keeping proper track of last FF form position.

FF programmers changed something in the latest FF update version.

Perhaps a more clear question is - FF app form no longer starts in the same location as last usage.

More detail - This occurred immediately after FF update. Prior to the update, when launch FF app, the form would return to the same location and size.

Now, it will not return to the same location, i.e. it now splits monitors, but at least it will retain the last used size.

I do not have the form maximized. It is at some reduced size.

FYI - I write app software, and know exactly what must be done in order to restore location and size when an app is started. That information must be kept in a file, or the registry. I also know that when an app starts, one cannot change size and location in the form constructor. The change must occur in the form Activated event (or some other event which occurs even later).

It may be possible that someone added new activity after the form location/size change operation, which may have moved the start location to the center of the virtual display area, virtual meaning the combination of whatever monitors are connected.

I tried rebooting the PC, in the event that Microsoft O/S locked the file down, so that it could not be updated. I have seen that happen a number of times. It takes a reboot in order to unlock the file. Same thing can happen with registry entries.

Reboot did not solve the problem.

hi, does it make a difference if you enter about:config into the firefox address bar (confirm the info message in case it shows up), search for the preference named browser.startup.blankWindow & double-click it and change its value to false?

That did indeed solve the problem. Thanks.