Affected versions

• Firefox 84.0b7
• Firefox 85.0a1

Affected platforms

• macOS 10.15.7 & 11.1

Steps to reproduce

1. Launch Firefox's profile manager and keep it open
2. Download the User.js from the attachments and open it (have the user.js to be opened by default by Firefox)

Expected result

• Nothing happens, as there is already one Profile manager opened

Actual result

• There is a small window with a search opened, and can't be closed, only if the Profile manager is completely closed

Regression range

• I will see for a regression if there is one.

Additional notes

• The issue can be seen in the following attachment
• Windows 10 is not affected (there is a second profile manager opened if user.js is launched), and Ubuntu won't let the user to open by default the file with Firefox.

Suggested severity

• S3

Sounds like an issue with the remoting implementation on macOS. I suspect the file launch is causing us to attempt to open a full browser window before we have a working profile but would need to dig further.

This is not a regression. I managed to reproduce the issue on macOS 10.13 using an older version of Nightly from 2016-08-01.