I was looking for something like this for a while, so here is how I made my own Firefox 'app' mode.

^{For Googlenauts with Windows/Mac 'Set Up Firefox' & 'Alternatively...' should also work on other OSs, perhaps with a few tweaks to the commands used, whilst 'Create Launcher' should work only for most Desktop Environments that implement the freedesktop 'specifactions'.}

Set Up Firefox

First run firefox --ProfileManager from terminal (you may need to close any running instances of Firefox first, or use the -new-instance option).
Create a new profile and call it app. Select the 'Default' one (IMPORTANT: otherwise by default it will start the app profile you are creating) and press 'Exit'.

Now run firefox -P app. This will start Firefox from the new app profile you just created. As removing the tabs and navigation bar is now difficult or impossible in Firefox's settings, you will need to install some extensions to remove them - these ones work, though may be better ones available that hide the bars permanently:

• Hide Tab bar with one Tab - hides the tab bar when there is only one tab open.
• Hide Navigation Bar - you need to press F2 to show/hide the nav bar

Edit: Both options of hiding the tab+nav bars is also included with Classic Theme Restorer - small icons can also be set for a more compact layout.

Now, when you run firefox -P app -new-instance http://URL (e.g. firefox -P app -new-instance https://askubuntu.com/q/487936/178596), you should get a Firefox window like this:

Also, when you open Firefox by running firefox or clicking the Firefox button, it should open your normal Firefox profile with the tab and nav bars.

Works in Firefox 30.0, 40.0, partially tested in 52.

Create Launcher

You probably want to create a launcher to open your app from the menu - you can do so using this template:

[Desktop Entry]
Name=<APP NAME>
GenericName=<APP NAME>
#Comment=Browse the Web
Exec=firefox -P app -new-instance <https://URL>
Icon=<ICON>
Terminal=false
Type=Application
#MimeType=text/html;text/xml;application/xhtml+xml;application/vnd.mozilla.xul+xml;text/mml;x-scheme-handler/http;x-scheme-handler/https;
StartupNotify=true
#Categories=Network;WebBrowser;
Keywords=<KEYWORDS>

Where:

• <APP NAME> is the name of your app
• <https://URL> is the URL you want shown by default on launching the app. -new-instance is optional but allows the Firefox App to be run as the same time as normal Firefox. See also: Mozilla Developer - Command Line options and the output of firefox --help.
• <ICON> is the name of a icon /usr/share/icons or ~/.local/share/icons, or the path to a icon file (preferably PNG or SVG I think).
• <KEYWORDS> - Relevant keywords delimited by ;, you can include words you can use to search for the launcher in the Dash/Menu - e.g. Paper;Ink;Toner; - Optional: comment it out with a # at the beginning of the line if you don't use this.

For more info on how .desktop files work, you can read this

You can also follow both above steps, and create various different app profiles, just remember if you use a different name to app - e.g. gmailapp, you need to use that name consistently instead of app.

Also, I'm not sure the -new-instance option is needed much any more, I have left it in anyway.

See also: - https://superuser.com/questions/468580/create-application-shortcut-chromes-feature-in-firefox

Alternatively...

I was looking for a solution to create a script so I could run a command and create Firefox apps (so without extensions etc), and the following userChrome.css works well at hiding all the toolbars:

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
#TabsToolbar,
#PersonalToolbar,
#BookmarksToolbar,
#MenuToolbar,
#tabbrowser-tabs,
#nav-bar,
#TabsToolbar { display: none !important; }

I haven't tested it too much yet, thought it will be annoying to use since it hides all the open tabs....

For that, there once was an addon called "Open Chromeless" – but it was removed from AMO. A work-around is described here; I've just checked it and it seems to work. Partly. Cannot get rid of the addressbar, and there's a frame around the window. If you can live with that:

1. Press Shift-F4 to open the Scratchpad

2. In the editor, enter

   window.open("https://superuser.com/", "_blank","width=800,height=600,resizable");
   

   (replace the URL with the one you want to use)

3. Click "Run" on the scratchpad toolbar

Now a new "chrome-less" window should open with the page specified. Resize it to your needs:

^{Screenshot of the "chromeless window" (click to enlarge)}

Right-click next to the addressbar, as shown in the screenshot, lets you disable the address bar as well (untick "Navigation toolbar") – but note that would remove it from your main window as well.

I'm aware this does not fully match your request (it's not launching from the command line, and leaves at least a frame around the window), but it comes as close as I could get to it.

Firefox 3.0 and higher have disabled setting location by default. resizable and status are also disabled by default. You can verify this by typing `about:config' in your address bar and filtering by "dom". The items of interest are:

• dom.disable_window_open_feature.location
• dom.disable_window_open_feature.resizable
• dom.disable_window_open_feature.status

You can get further information at the Mozilla Developer site. What this basically means, though, is that you won't be able to do what you want to do.

One thing you might want to do (though it won't solve your problem), is put quotes around your window feature parameters, like so:

window.open('/pageaddress.html','winname','directories=no,titlebar=no,toolbar=no,location=no,status=no,menubar=no,scrollbars=no,resizable=no,width=400,height=350');

In Firefox:

You can find details of the Firefox "Command Line Options" on MDN.

It appears you can not do exactly what you desire, if you want to continue to have the page opened under your normal profile and without having your normal use of that profile disturbed. If you are willing to use a separate profile which is used only for this task, then you can accomplish what you desire. Using another profile is not a big deal. I commonly have more than one running at a time, and even use different versions of Firefox running at the same time under different profiles.

Using a separate profile and add-ons:

To create a new profile see: Use the Profile Manager to create and remove Firefox profiles or Multiple Firefox profiles. Create a profile, choose a name.

You will need some add-ons:

• Hide Navigation Bar (change options (Tools->Add-ons then "Extensions" and the "options button for this extension. Select "When Firefox starts: Hide the Navigation Bar")
• Hide Tabbar (change options to select "Auto hide when only one tab is open")

There may be others you could use, but the combination of these two worked when I tested it.

Go to the page you want to see. Adjust the size and position of the window to what you desire. By right clicking the mouse in the toolbar area de-select "Menu Bar" and "Bookmarks Toolbar". Close Firefox. Firefox should automatically remember the size and location of the window.

Create a shortcut:

  "C:\Program Files\Mozilla Firefox\firefox.exe" -no-remote -P "My Profile Name" -url "http://the page I want to see"

Click on the shortcut. That should work.

Shameless plug: If you want the icon for the window to be different so you can tell the windows apart in the taskbar, you could use: Change Profile's Window Icons. An extension whicht arose from my answer to a stackoverflow question. If you do change the icon, you will probably want to change the properties for the shortcut to point to the icon you use.

Getting close to what you want using your current profile without disturbing it:

Without using an add-on you can come close. [Note: all were tested in Firefox and a Windows operating system assumed (for file paths).]

You could use a bookmarklet to open a static URL in a limited window :

javascript:void(window.open("http://www.google.com","_blank","outerWidth=400,outerHeight=200,top=500,left=600,menubar=no,toolbar=no,location=no,personalbar=no,status=no,resizable"))

or the URL you are currently viewing:

javascript:void(window.open(location.href,"_blank","outerWidth=400,outerHeight=200,top=500,left=600,menubar=no,toolbar=no,location=no,personalbar=no,status=no,resizable"))

You can have the window open from a desktop shortcut, but in order to have the window with a limited interface you will end up with a normal size window which you will have to close (scripts are not permitted to close windows which are not opened by a script). You would need to use an html file on your machine to contain the script to open the appropriate URL.

Note the first time you do this Firefox will inform you that it blocked a popup. You will need to permit popups from that file URL.

Example HTML file (example assumes it is located at: C:\open_location.html):

<head>
    <script class="code" type="text/javascript">
        var features =  ""  
                        + "menubar=no,toolbar=no,location=no,personalbar=no"
                        + ",status=no,chrome=yes,resizable,centerscreen"
                        //+ ",width=400"        //Width of content window
                        //+ ",height=200"       //Height of content window
                        + ",outerWidth=400"   //Width of window
                        + ",outerHeight=200"  //Height of window
                        + ",top=500"
                        + ",left=600"
                        ;
        window.open("http://www.google.com/","_blank",features);
        //Can only close windows opened by script.
        //window.close();
    </script>
</head>
<body>
</body>

You could then use a shortcut that opens the URL of that file:

"C:\Program Files\Mozilla Firefox\firefox.exe" -url "file://C:/open_location.html"

I would suggest using a separate profile:

"C:\Program Files\Mozilla Firefox\firefox.exe" -no-remote -P "My Profile Name" -url "file://C:/open_location.html"

You can get rid of the URL bar from all of the above by setting dom.disable_window_open_feature.location=false in about:config. However, if you do that I recommend using a different profile which is used for this purpose only as you normally don't want to do such for normal use.

I'm using a self-written stylesheet to achieve that purpose for Firefox.

It hides the complete top-bar and appears when hovering over the top window-border, or focusing the address-bar with the key-combination Ctrl+L.

It's not perfect (e.g. there can be a flickering effect when focusing the address-bar, or after clicking the hamburger-symbol to open the menu, you need to use the Arrow-Down-key for selecting a menu-item) but works for me:

https://github.com/ida/skriptz/blob/dde60dadcca5bb45ce6ca14bb74373637f31a309/setup/browser/ff/userChrome.css