Manage site list panel always shows a scrollbar even when it's not needed

[groovecoder]

Before submitting a bug report

• I updated to the latest version of Multi-Account Container and tested if I can reproduce the issue
• I searched for existing reports to see if it hasn't already been reported

Step to reproduce

1. In the browserAction popup, click "Manage Containers"
2. Click a container (e.g., Personal)
3. In the container panel, click "Manage Site List..."

Actual behavior

1. The panel of assigned sites DOES show a scrollbar even though it's not needed
2. With the new Reset cookies in site manager feature, the scrollbar covers up the trash can icon for "Remote this site"

Expected behavior

The panel of assigned sites should not show a scrollbar if it's not needed

Additional informations

No response

Provide a copy of Troubleshooting Information page (optional)

No response