Webcompat Blipz Experiment icon is wrongly displayed in Private browsing mode

[SoftVision-EmilPasca]

[Affected versions]:

• Firefox Release 60.0.2
• Firefox 61.0b13

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have the "Webcompat Blipz Experiment" installed though "about:debugging".
• Have the "extensions.webcompat-blipz-experiment.variation" pref created in "about:config" with the value "more-context".
• Have the browser console open.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Open a new private window (Ctrl+Shift+P).
3. Navigate to https://www.google.com or any another website which is in the blipz list .
4. Observe the address bar.

[Expected result]:

• The "Webcompat Blipz Experiment" icon is not displayed.

[Actual result]:

• The "Webcompat Blipz Experiment" icon is displayed.

[Notes]:

• The popup can be also accessed when clicking on the "Webcompat Blipz Experiment" icon.
• Telemetry pings are also send when opening the pop-uo.
• This issue is also reproducible with other variations ("no-context" and "little-context").
• Attached a screen recording of the issue:
  

[miketaylr]

As long as the addon never initiates a prompt for a user in private mode, this is OK. We still allow a user to self-report in private browsing mode.

(Sorry if this wasn't clear)