Please update to Firefox 19 and try there Update Firefox to the latest release

you can either install the searchreset addon to get rid of the problem or manually reset the page that opens on each new tab: enter about:config into the firefox location bar (confirm the info message in case it shows up), search for the preference named browser.newtab.url and right-click &reset its value to the default (about:newtab).

After update to 19 and restart, new still displays google home page and not thumbnail views of Most Visited web sites.

Tried the about:config procedure earlier and browser.newtab.url was already defined as about:newtab

can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here...

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

You can check for problems with preferences and try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default values.

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

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

• Help > Troubleshooting Information > Profile Directory: Show Folder

Found that be clicking the link about default (upper right of window) on newly opened tab and selecting to restore tab defaults and clicking OK, my thumbnail displays of Most Visited sites were restored.