[Affected versions]:

• Firefox Nightly 72.0a1 - Build ID: 20191114055112

[Affected Platforms]:

• All Windows
• All Linux

[Prerequisites]:

• Have the latest Firefox Nightly installed.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites and wait ~5 minutes.
2. Observe the "What's New" toolbar button displayed in the right part of the "Address Bar".

[Expected result]:

• A blue badge is displayed in the top-left part of the "What's New" toolbar button.

[Actual result]:

• The blue badge is displayed in the top-middle part of the "What's New" toolbar button.

[Regression Window]:

• Considering the fact that this issue is not reproducible with the Firefox Nightly build from 11/12/2019, using the mozregression tool I have managed to find the following regression:
  Last good revision: 9e3f44e87a1a2be927c7fab135653c6b86b982c9 (2019-11-12)
  First bad revision: 35436d4e7917bf9d9b96a6173201ca001a8ff7bc (2019-11-13)
  Pushlog:
  https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=9e3f44e87a1a2be927c7fab135653c6b86b982c9&tochange=35436d4e7917bf9d9b96a6173201ca001a8ff7bc

[Notes]:

• This issue is reproducible on the "Firefox Account" toolbar button.
• This issue is also reproducible with all the add-ons that have a toolbar button with notifications.
• This issue is not reproducible on macOS.
• Attached a screen recording of the issue.

Andrei, could you please give us your opinion regarding this issue?

I think this is the same issue as bug 1596176.

I have verified that this issue is no longer reproducible with the latest Firefox Nightly (72.0a1 Build ID - 20191115095319) installed, on Windows 10 x64 and Ubuntu 18.04 x64. Now, the badge is correctly displayed in the top-right part of the "What's new" and "Firefox Account" toolbar buttons.