Do this once in Firefox:
Type "about:config" in the Location bar, then search for
dom.disable_window_open_feature. Sort by value to see any set to true, then
double click to set to false. For instance, I changed status, resizable, and
location.
Enable pop-ups.
Each time you want to launch the two windows go to Tools->Web Developer->Web Console and paste in javascript commands like these:
window.open("http://superuser.com/questions/782653","_blank","left=0,top=0,outerheight=768,outerwidth=675,dialog,close")
window.open("http://developer.mozilla.org/en-US/docs/Web/API/Window.open","_blank","left=675,top=0,outerheight=768,outerwidth=680,dialog")
I've done this on OSX with pretty good results. I expect with DWM it'll work
even better, but you may have to look through the Window.open docs to see which
settings to use. Notice that many features default to "no" when the Window is
opened like this, which is why I didn't use "location=no", etc.
It should be straight-forward to write an html file that will launch this js code automatically:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<script>function create_windows () {
window.open("http://superuser.com/questions/783164","L","left=0,top=0,outerheight=768,outerwidth=675,dialog,scrollbars,close");
window.open("http://developer.mozilla.org/en-US/docs/Web/API/Window.open","R","left=675,top=0,outerheight=768,outerwidth=680,dialog,scrollbars");
}</script>
</head>
<body onload="create_windows()">
Close this window, or reload to reset left and right windows.
</body>
</html>