Trovi requires some extra steps to remove.

(1) Start with the Windows Control Panel, Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Take out as much trash as possible here.

(2) Then, in Firefox, open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Set nonessential and unrecognized plugins to "Never Activate".

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Now... can you successfully change browser.newtab.url? If necessary:

(3) Search for remaining issues with the scanning/cleaning tools listed in our support article: Troubleshoot Firefox issues caused by malware. These on-demand scanners supplement your Norton software and often are more aggressive when it comes to "annoying" software that Norton doesn't detect as a threat.

Success?

Thank you very much. I was suckered into downloading a video player a while ago and it also installed PC Speed Maximizer without my consent. I uninstalled all programs that were new but apparently they left a host of garbage spread all over the hard drive. When I saw your reply I followed your directions but didn't find any programs or Firefox add-ons that were unusual so I downloaded Malwarebytes and it found 287 exceptions all of whose names started with PUP.Optional. These were quarantined and Firefox started working as it should without even having to reset the browser.newtab.url Again, thanks.