Only Google search engine is supported when clicking the Voice Fill button from the toolbar

[SoftVision-CarmenFat]

[Affected versions]:

• Firefox 56.0.2 and up
• Voice Fill v.1.3.4

[Affected Platforms]:

• All Windows
• All Linux
• All Mac

[Prerequisites]:

• Have a Firefox profile with the Voice Fill (v. 1.3.4) experiment installed.
• Have other Voice Fill supported search engine as default (DuckDuckGo or Yahoo).

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Click the Voice Fill button from the toolbar and observe what happens next.

[Expected result]:

• A new tab with the default search engine page is opened and Voice Fill overlay is triggered, as well as the permission prompt.

[Actual result]:

• A new tab with Google search engine is opened and Voice Fill overlay is triggered, as well as the permission prompt.

[Notes]:

• Since we already have support for various search platforms (Yahoo, DuckDuckGo), the Voice Fill button from the toolbar should open a page with the default supported search engine.
• Attached a screen recording of the issue: