Steps to reproduce:

1. Open www.nu.nl in either Firefox 58 or Chrome
2. Open the elements list
3. Press tab, and enter a word to filter on
4. Press shift+tab

Expected behavior:

The list properly filters.

Actual behavior:

Multiple LookupErrors are raised.

System configuration:

NVDA version: Both 2017.4 and next
NVDA Installed or portable: Installed
Windows version: Windows 10 fall creators update

Other questions:

Does the issue still occur after restarting your PC?
Not yet tested, but we should catch these LookupErrors anyway