Multi-account-containers: [Windows] A part of the current tab's title is wrongly displayed in the "Edit Containers" panel, after you move the window while the edit panel is open

[Softvision-CristinaBadescu]

[Affected versions]:

• Multi-Account Containers 6.0.0
• Firefox 59.0.1 and above

[Affected Platforms]:

• All Windows

[Prerequisites]:

• Have a Firefox profile with the latest "Multi-Account Containers" add-on version (6.0.0) installed.

[Steps to reproduce]:

1. Open the browser with the profiles from prerequisites, navigate to https://brightside.me/ and click the "Multi-Account Containers" button from the browser toolbar.
2. Click the "Edit Containers" button and move the window.
3. Click again the add-on toolbar button and click the "Edit Containers" button.
4. Observe the edit panel.

[Expected result]:

• The edit panel is correctly displayed.

[Actual result]:

• A part of the current tab's title is wrongly displayed above the containers list.

[Notes]:

• You might need to repeat several times steps 2 & 3 to encounter this issue.
• Here is a screen recording of the issue:
  

[Paarmita]

@Softvision-CristinaBadescu I tried this many times by changing the window location and trying clicking edit button several times, but I couldn't reproduce this error.

[groovecoder]

Unable to reproduce; this seems to be fixed now.