Hi  !

As you probably will have guessed  : that Search Incognito is a browser hijacker.

Go to the 3-bar menu (or   'Tools') => Addons => Extensions and look for any unfamiliar or suspicious looking extensions, like e.g. :

SafeSearch Incognito (of course  !) SearchAssist Incognito Search for Fire Fox 1.6 SafeSearch ch SafeSearch net Converter.onesearch org File Convertor and Search Addon Findwide Search Engine 1.7

When you find any : remove them.

Do the same in your system's Control Panel.

However :   most malware will be 'hiding' somewhere , so let's run malware scans :

Further information can be found in this article :
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners.
They all work differently   -   what one program doesn't pick up, the other might.

Also see : http://removeallthreats.com/how-do-i-get-rid-of-search-incognito/

Especially for Mac : https://www.malwarebytes.com/mac/

Thanks refreshing firefox appears to have cured it, will run some of the malware later much appreciated

RichJJ said

Thanks refreshing firefox appears to have cured it, will run some of the malware later much appreciated

My pleasure  ! Running those malware scans : good decision  ! Better safe than sorry, eh  ?