I've taken that and added a bit to make it functional. Based on the way ScriptDownloader works, the install dialog is attached to the browser window, not the addons window. But that's probably good enough for now.

http://github.com/arantius/greasemonkey/compare/master...issue_1142

Basic support for drag/drop user scripts on the addons window to install.

Closed by dd22c58

I'm not sure we can close this since it's not getting past the first line of GM_installUri.

Indeed.

Error: Cc is not defined
Source File: chrome://greasemonkey/content/utils.js
Line: 376

Whoops!

Well, correcting the Cc and Ci references, because this function is sometimes used outside the component where they're defined, is easy.

But now, I'm seeing tons of crazy bugs. Perhaps a Linux thing, I didn't first develop this on Linux, but that's where I am now. I've pushed the easy fix, so it should show up in the next nightly. Then I'll have to dig into these bugs.

I can confirm the weird behavior you noticed under Linux.
I slightly modified urlFromDragEvent (see below) so it doesn't throw an exception when mozGetData no file, and it appears like everything works fine as long as I hover the file over the tab.
But as soon as I drop the file, FF throws Gtk-CRITICAL **: gtk_drag_get_data: assertion `GTK_IS_WIDGET (widget)' failed, file instanceof Components.interfaces.nsIFile returns false and instead file is just a string of UTF-8 characters or null.
Though this bug isn't 100% reproducible - sometimes FF doesn't throw that Gtk-exception, and then installing the script by dropping it works just fine.
So it looks like this weird behavior is actually a bug in Firefox itself.

The relevant part I changed in urlFromDragEvent:

var file = event.dataTransfer
    .mozGetDataAt('application/x-moz-file', 0);
if (file instanceof Components.interfaces.nsIFile) {
  url = GM_getUriFromFile(file).spec;
}

Reimplement with nsDragAndDrop, which works cross platform.

Closed by 98d0b3b

Is it known that feature issue is no longer working in master (drop script from filesystem anywhere, ff3.6)

Error: uncaught exception: [Exception... "Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIXPCComponents_Utils.import]" nsresult: "0x80520012 (NS_ERROR_FILE_NOT_FOUND)" location: "JS frame :: chrome://greasemonkey/content/scriptdownloader.js :: anonymous :: line 74" data: no]

What is easily accessible now to test, Mozilla/5.0 (Windows NT 6.1; rv:5.0) Gecko/20100101 Firefox/5.0 works fine.

Could you provide an exact user-agent string like this where you're seeing failure?

Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12 with the old addons manager, maybe it's just the build I'm using. Dropping a script on the userscripts tab of the addons manager, clicking the install button does not dismiss the dialog, clicking it twice removes the script, and sometimes even though the script sometimes gets into the addons list, it will not stay there after restart.

1.  Cu.import("resource://greasemonkey/GM_notification.js", tools);
   

K. This bug was the new manager, and in 0.9.0. For the old one: #1381

Dropping a script on the userscript tab of the addon manager of FF5 results in "this addon could not be installed because it appears to be corrupt"

Same problem here.