When start up times are longer than 20 seconds on average, a user is shown a warning message that makes Firefox sound defective. Most often, refreshing the profile helps to improve start up time and resolve these issues.

Improve the messaging to "Refresh Firefox for optimal performance." (remove Mozilla Firefox seems slow... to... start.)
Explore Refresh Firefox button in the warning.
Change button: "Learn How to Speed It Up" to "Refresh Firefox"
--> same button seen on this page: https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings to initiate refreshing
Change button: "Don't Tell Me Again" to "Dismiss" resulting in same action

"Dismiss" seems to duplicate the X button. It's not clear that "Dismiss" would suppress the message in the future.

Then I recommend not using title case and changing to "Don't tell me again"

(In reply to Dão Gottwald [::dao] from comment #1)

"Dismiss" seems to duplicate the X button. It's not clear that "Dismiss" would suppress the message in the future.

Michelle: Can you weigh in on the proposed string?

Jared: I think you originally implemented this, do we still have concerns about directly triggering a refresh? (i.e. potentially dataloss scenarios) If so, I would recommend we only tweak the string.

(In reply to Justin Dolske [:Dolske] from comment #3)

Michelle: Can you weigh in on the proposed string?

Jared: I think you originally implemented this, do we still have concerns about directly triggering a refresh? (i.e. potentially dataloss scenarios) If so, I would recommend we only tweak the string.

Worth noting that the current mechanism of triggering refresh (which would be the easy option for implementing this) always shows a confirmation dialog first.

https://searchfox.org/mozilla-central/source/toolkit/modules/ResetProfile.jsm#46

(In reply to Justin Dolske [:Dolske] from comment #3)

Jared: I think you originally implemented this,

I did.

do we still have concerns about directly triggering a refresh? (i.e. potentially dataloss scenarios) If so, I would recommend we only tweak the string.

I'm personally still concerned about it. The original implementation linked to https://support.mozilla.org/en-US/kb/firefox-takes-long-time-start-up which suggests different solutions to startup being slow, as there can be different causes. It was later changed to link directly to the Reset Firefox article, but afaik we have no hard data on the reset helping most users in that situation. See also the discussion in bug 872172.

We removed the slow startup notification bar as part of the Proton work, so I think this bug is now INVALID.