Jira Burndown Gadget render extra space after each refresh in Firefox

Issue Summary

Jira Burndown Gadget render extra space after each refresh in Firefox

Environment

Confluence 6.15.9
Jira 8.3.3, 8.3.4
Firefox 72.0.1 (64-bit)

Steps to Reproduce

Replicate this using Firefox browser

1. Setup Application Link between Confluence and Jira
2. Add Burndown Gadget from Jira to Confluence
3. Insert a Burndown Gadget into a Confluence page
4. Waiting for the auto-refresh that is configured or click on the Refresh button manually

Expected Results

Burndown Gadget refreshed with exact same width and length

Actual Results

Burndown Gadget gain 40px white space at the footer of the gadget on each refresh
Jira Burndown Gadget.mp4

Information

This behavior is not observed in Jira 7.11.1

Workaround

Browse Confluence using alternative browser such as Chrome