Geocoder widget auto-complete not visible at times

Greetings,

I had just begun working to add a custom Geocoder service and saw your new feature added in 1.30. I downloaded the latest candidate today (Cesium-1.29.0-master.19674.zip) and tested with that.

Works great, except there is one case with Firefox where the auto-complete window is not visible when it should be. Here are the steps to reproduce:

1. Click on search box
2. Type search terms (auto-complete visible as expected)
3. Hit enter
4. Map position changes to searched location (as expected)
5. Press Ctrl-A / Command-A (shortcut key to select all text)
6. Type other search terms (auto-complete is NOT visible as expected)

A work around is to click the search text field again instead of Ctrl-A / Command-A as in Step 5. Then it will work as expected.

I was not able to reproduce this error in Safari or Chrome. I believe that the reason was that after Step 3, the search text field no longer had focus, and a mouse click was required before additional search terms could be entered.

Here's a demo:
https://www.youtube.com/watch?v=rctgl6pKxK0&feature=youtu.be

Start by reproducing the steps in Firefox, focusing on what happens to the search field after pressing Enter and then Ctrl-A or Command-A. Inspect the Geocoder widget's focus and auto-complete behavior. Done means new search terms consistently make the auto-complete window visible, while preserving the existing behavior in Chrome and Safari.

Written by the indexing model from the issue text.