To answer your question . . . some of us here are on the dev team while other devs stay on mostly irc and rarely come here.

thank you golinux

It sounds like the window could be getting accidentally "shaded" via a mouse action.

As I recall, double left clicking or scrolling the scroll wheel on the window title bar causes the window to roll/up down.  You could also temporarily switch to window decorations which support the shade button for a while and see how it goes.

Yup! You are right guys.

The first time was with both touch pad and external mouse activated at the same time and accidentally touching the touch pad. Couldn't understand what happened. I now tried vertically on the right edge of the touch pad with the mouse pointer over the title bar and there we went To avoid confusion a 'shade' button with Clearlooks-Phenix-Purpy would be nice .

Thank you very much for your help.

On the side. I am wondering who on the forum who are also Devuan developers? I checked the forum user list, but it does not mention.

Anyhows I would like to express my great appreciation and say thank you for the Devuan project. My first real encounter with GNU/Linux was Debian some years ago where I also tried gNewSense, but then systemd came along and all related to GNU/Linux came to a halt. So when I found out about Devuan I was very pleased. Have been monitoring the releases since alpha/beta stages and are now for the first time getting to know how it works. So then having the experience that Devuan is the most responsive system that I have ever used, has been a delightful experience. When working with different systems one get a intuitive feel for how well hardware and software works together, and Devuan gives me a very pleasant feel. As a comparison I was working with NT-networks back in the 90's and I have never been satisfied with any MS system up to and included Win10. So I hope and wish for a long and lasting life for the project

It sounds like the window could be getting accidentally "shaded" via a mouse action.

As I recall, double left clicking or scrolling the scroll wheel on the window title bar causes the window to roll/up down.  You could also temporarily switch to window decorations which support the shade button for a while and see how it goes.

Yes, there is no action button in the title bar but Clearlooks-Phenix-Purpy does shade with the scroll wheel and you might have accidentally done that.

As I recall, double left clicking or scrolling the scroll wheel on the window title bar causes the window to roll/up down.  You could also temporarily switch to window decorations which support the shade button for a while and see how it goes.

Also do you have redshift/blueshift installed?

I am not sure what 'redshift/blueshift' is, so I guess that I have not installed it/them

Is this in LXQT?
Are you running Jessie?
Which firefox do you have?
Have you upgraded recently?

Thanks for your prompt reply fungus.

It is Xfce 4.10 with Devuan Jessie 1.0.

Firefox version is 52.5 which was upgraded the day it was released I guess. Have a habit of doing a 'update/upgrade' almost every day. When you ask, I am suddenly uncertain as to how long ago the first instance was..... So it could be that both instances has been with 52.5, the first time not with 52.4

I am not sure how this happens, but it has happened twice within a weeks time.

The style and wm theme is both with default Clearlooks-Phenix-Purpy.

The behaviour is just like as if a 'shade' button in the title bar was used, but as you know the Clearlooks-Phenix-Purpy theme does not have a 'shade' button.

When maximizing the 'window' the titlebar jumps up to top edge of the screen as it is supposed to do, but there is no Firefox window. It is just the desktop. When maximizing there is no grey line under the title bar.

The only solution that I have come up with is to close Firefox and start over.

Any ideas?

Thanks