Hi James,
Thank you for the update.
I am afraid that I was not able to reproduce the issue in Fire Fox. Please refer to the following steps that I tried to reproduce it.
1. Created a sample with menus.
2. Run the sample
3. Hover over a menu item and then move down over the menu that pops up
4. But multiple things are not selected on the menu and also menu does not stay on screen
5. And also did not get the error ERR: null == m_oPinnedPanels[Menu2_P1].
Also I have created a simple sample to test this issue and it is available in the following link.
http://websamples.syncfusion.com/samples/Tools.Web/5.1.0.51/65348/main.htmPlease have a look at the above sample and if still the issue exists, could you please try reproducing it in the above sample or send us the reproducing steps so that we could sort out the cause of the issue and provide you a solution?
Thanks,
Melba