Fix performance bar from sticking on Firefox

What does this MR do?

On Firefox, the Gitlab performance bar console log sticks in the devtool console so Firefox users have to keep scrolling down after every page load to go back to the default tailing of new console logs. This commit fixes this.

Screenshots (strongly suggested)

before (sticks at this part)	after (no longer sticks—screenshot is to show how the Gitlab performance bar now looks)
Screen_Recording_2021-01-20_at_10.31.56_am	Screen_Recording_2021-01-20_at_10.33.50_am

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team