"Facebook Container" string is duplicated in the overflow menu

[GeorgiuCiprian]

Affected versions

• Nightly 68.0a1
• Release 66.0
• Release 65.0

Affected platforms

• Windows 10 x64
• macOS 10.13
• Ubuntu 16.04 x64
• Win 7 x86

Steps to reproduce

1. Install the facebook_container-1.6.2-an+fx.xpi from here
2. Pin the Facebook Container's icon to the overflow menu.
3. Open the add-on from the overflow menu.
4. Inspect the "Facebook Container" strings.

Expected result

• The "Facebook Container" string is displayed only once.

Actual result

• The "Facebook Container" string is duplicated.

Additional notes

• please see the attached image:

[maxxcrawford]

This still reproducible on the latest version of the add-on (2.1.1) and Firefox (77.0.1).