Does this occur on another browser on your mobile device? Can you try uninstalling Firefox then reinstalling it on your mobile device to see if it helps or not?

I don't have a mobile device - that's why it's a nuisance. No other browser either.

This could be set as your homepage? See How to set the home page to check.

Firefox is my default browser and it's connected to that somehow. I have Yahoo as my homepage. This program showed up when I downloaded the latest version of Firefox.

Your homepage has nothing to do with Firefox being your default browser. Did you read the hyperlinked support page?

I've read so many pages and nothing explains how to get rid of Marketplace.firefox.com

Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Use a compressed image type like PNG or JPG to save the screenshot.

So your home page setting is correct?

• Tools > Options > General > Startup: Home page
• https://support.mozilla.org/kb/How+to+set+the+home+page

If you do not keep changes after a restart then see:

• http://kb.mozillazine.org/Preferences_not_saved

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes