When I open a new tap Firefox tries to open a non existant address how can I change this please

When I try to open a new tab I get this: Server not found

         Firefox can't find the server at www.[r;;iåvÞyevq¾qîx»ò
 Check the address for typing errors such as instead of
 If you are unable to load any pages, check your computer's network
 If your computer or network is protected by a firewall or proxy, make sure
   that Firefox is permitted to access the Web.
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