hello, you can try to use the search reset addon.

If there is a problem with the about:home Home page then try to reset the search engine used on the about:home page.

Reset the browser.startup.homepage_override.mstone pref via the right-click context menu to the default on the about:config page and close and restart Firefox to restore the about:home page to its default.

• Open the about:config page via the location bar
• Type in the Filter bar: mstone
• Right-click the browser.startup.homepage_override.mstone line and select: Reset
• Close and restart Firefox

If that didn't help then delete the delete the chromeappsstore.sqlite file in the Firefox Profile Folder and repeat the above.

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder

Thanks for the suggestion, madperson. Unfortunately, it was ineffective in my case.

Thanks very much for the help, cor-el. It looks like your directions worked perfectly!

ok sorry - from the describtion of the addon i tought it is also covering the browser.startup.homepage_override.mstone preference, but glad you got it working again!