[Windows] Formatting option tooltips are wrongly displayed on the latest Nightly

[SoftVision-EmilPasca]

[Affected versions]:

• Nightly 56.0a1, Build ID: 20170711030203

[Affected Platforms]:

• All Windows

[Prerequisites]:

• Have a Firefox profile with the latest Notes add-on (version 1.5-dev) installed.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Hover the formatting option buttons("Bold","Italic","Ordered list", etc.) from "Notes" sidebar.
3. Observe the displayed tooltips.

[Expected result]:

• The tooltips are displayed correctly below the corresponding buttons.

[Actual result]:

• The tooltips appear very far to the right of the button.

[Regression]:
With Nightly 56.0a1, Build ID: 20170710030203, the issue is not reproducible.
Last good revision: 392ed89ec2730a48d10b1cec741e86a242d28aa3
First bad revision: a625a2e9b3333a8e76982ea65f077cfded6ac224
Pushlog: https://goo.gl/N1DhXR

[Notes]:

• Attached a screen recording of the issue:
  

[vladikoff]

Wow! Firefox bug?

[Natim]

Yes :)

[Natim]

@SoftVision-EmilPasca Can you file this bug in bugzilla?

[SoftVision-EmilPasca]

Refs https://bugzilla.mozilla.org/show_bug.cgi?id=1380294

[SoftVision-EmilPasca]

The issue is no longer reproducible on the latest Nightly 57.0a1, Build ID: 20170807113452.