edit - whoops, I just saw a screenshot in another thread which shows that message bar, (which I haven't seen yet). Any chance that you are clearing cookies when you close Firefox?

The following answer that I posted a few minutes ago probably won't affect that message bar.

Are you referring to the message on the default homepage - about:home - below the search container?

That is a promo "snippet" which will run for a short period of time. It will go away in a few days or so.

The easiest way to avoid seeing messages such as that below the search container and avoid having the Firefox logo [above the search container] from getting substituted is to just set your own homepage and not use the "default" about:home page. See - How to set the home page

Many of us have disabled the changes to the top part [brandLogo portion] of the Firefox Start Page and turned off the promotional "snippets" [below the Search container] that Mozilla is using frequently now, so we don't see that "stuff".

If you feel venturesome, here's how to "fix it". Type about:config in the Location Bar and hit Enter. Accept the "dragons" message to see the advanced prefs screen. Use the Search field at the top to enter the pref mentioned below.

You can set the browser.aboutHomeSnippets.updateUrl pref to an empty string to stop your Firefox from retrieving "snippets" and brandLogo changes. Right-click that pref and select Modify then clear the Value for that pref in the box that appears, then click OK. That will also disable the "snippets" that appear below the Search container on the default homepage.

Then you need to open your Profile folder, via Help > Troubeshooting Information > Profile folder >> Show Folder button. Then close Firefox. With your Profile folder open and Firefox closed ("3-bar" Firefox menu button > Exit/Quit), wait minute or so, then delete the storage\moz-safe-about+home folder in the Firefox profile folder to remove the brandLogo and snippets stored in IndexedDB to make Firefox use the default brandLogo and a default snippet set.

Then restart Firefox for those changes to take effect.

If you should later change your mind about those modifications, you can reset the browser.aboutHomeSnippets.updateUrl pref via the right-click context menu and use Reset to get the default value back to start using the storage\moz-safe-about+home folder again.

I noticed at least 10 other people with the same problem after I posted this question. No solutions so far, sadly.

Any chance that you are clearing cookies when you close Firefox?

Sorry, more information has come in.

That is a message from the Heartbeat feature. It's experiencing a bug right now. Best to disable it so you can get some immediate relief.

To disable Heartbeat: Open about:config in a tab then search for browser.selfsupport.url and double-click it & set it to a blank value.

You may need to restart Firefox for the change to take effect.

Awesome. I'll give it a go. Thanks. :)

Hey folks. The bug has been fixed in Heartbeat and you should not see the prompt anymore. While I can understand that it was annoying, I would not suggest disabling the browser.selfsupport.url feature permanently.

Heartbeat is the main conduit we have for communicating with our users. Based on the responses we get to our ongoing Heartbeat research programs we are changing the future of Firefox. We are committed to building products for our USERS. The only way for us to do this is to communicate with our awesome user base on a regular basis.

So please consider turning Heartbeat back on now that the issue has been fixed. If you see a Heartbeat prompt asking you for feedback, please considering replying. We want to hear from you!