hello, please go to firefox > addons > extensions & disable/remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and run a full scan of your system with the security software that you have in place and different other tools like the free version of malwarebytes & adwcleaner.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

afterwards install the search reset addon - it will revert the most common customizations those adware programs do in firefox back to the default: https://addons.mozilla.org/firefox/addon/searchreset/

I tried to disable Smarbar but the next time I started a browser, it was still there.

Moreover, "Smartbar" did not show up in either Windows Control Panel or the more powerful (and great) Revo Uninstaller so I could not delete it this way. Still, I could see in the Activity Monitor that Smartbar.exe was running and that it was found in C:\users\<user>\AppData\Smartbar.

So I tried to delete that very folder but Windows said it had a programme running. I had already killed Smartbar.exe so, to find out if there were more programmes, I ran StartUp Delayer from r2 studios (another great programme) and immediately noted that an update programme related to Smartbar was scheduled to start every time I started the computer.

So, within StartUp Delayer I removed that programme completely from the start up schedule. Then I restarted my computer and at last I could delete the entire Smartbar folder mentioned above.

In my case I have backtracked the source of this terrible malware to CNET, a site which I until then had no doubts would be a reliable one.