Created attachment 300935 [details]
Debug file with possible showing why happening this issue

Dear Joanie,

I see an interesting bug after Firefox update from 36.0 to 37.0 release, possible this is a Gecko issue.
When in Firefox or Thunderbird I activating context menu and enabled the speak child position check box and speak tutorial message related check box, after Orca says the menu rolename, speaks a false position index value and a submenu related tutorial message.
Testcase:
1. Launch Firefox or Thunderbird, and enable in Orca preferences dialog both the speak child position and tutorial message related check boxes.
2. Press the context menu button your keyboard, click right mouse button or press SHIFT+F10 keystroke.
Expected result:
Because this situation in Firefox and Thunderbird the first menu is not selected by default, Orca need speaks only the menu rolename.
Actual result:
I always hear this situation after Orca speaks the menu rolename a false position index value and a submenu related tutorial message. If I press down arrow key, Orca right speaks the first menu item in the context menu.
The Orca 3.14.3 version doesn't producing this issue, speaks only the menu rolename and the tutorial mesage after the context menu pop up the screen.
My environment related informations:
OS: Ubuntu 14.04.2, Manjaro 0.8.12 GNOME community edition:
Orca version: latest master branch version with Ubuntu 14.04.2, gnome-3-16 branch of my Manjaro system
Affected Orca branches: master, gnome-3-16

I attaching a debug.out file. Look the debug file after the 1802 line. The debug file I created with Orca latest master branch version.

Attila