Previous session displayed when trying to do a blank search

[alexandra-martin]

Prerequisites:

Mic permissions are enabled.

STR:

1. Click on the mic icon from the browser toolbar.
2. Write a command, e.g. "search fox", press "Enter" and wait for the result to appear in the "Doorhanger".
3. Click the "Back" button.
4. Delete the previous "search fox" command.
5. Press "Enter".

Expected result:

The "Doorhanger" has a notification that no match is found.

Actual result:

The "Doorhanger" displays the previous search result.

Notes:

Reproduced on Mac 10.14.6 with Firefox Nightly 71.0a1 (64-bit).
Reproduced also in the following circumstance, shown in the second gif:

• after the result appears in the "Doorhanger", the "search fox" command title is deleted while in session, like in 192, the "Back" button is clicked, then "Enter" is pressed (blank search).

[awallin]

Likely related to #170 and other back button issues.

[alexandra-martin]

The bug is still reproduced on Mac 10.14.6 and Win10x64 with Firefox Nightly 71.0a1 (64-bit).

[alexandra-martin]

Verified on Mac 10.14.6 and Win10x64 with Firefox Nightly 71.0a1 (64-bit).