Summary

The Slack panel may throw a 'Client-side error' in Firefox.

Steps to Reproduce

1. Have a Slack message with more than three lines;
2. Attach this message in a Jira issue.
3. Access this issue using Mozilla Firefox.

Expected Results

The Slack panel is loaded correctly:

Actual Results

There is a Client-side error in the UI and the Slack panel does not load:

Workaround

Use a different browser.