Is this Windows, (which one), or Mac, Linux?
If this is Windows, next steps to try.
1] Task Manager
Open the Task Manager, (right click the Taskbar, select Task Manager). In the new window select the Processes tab. Make sure you click "Show processes for all users" at the bottom. Search down the list for any entry that looks like MyStart and/or Incredibar. If you find any, select the entry then "End process". That's a temporary measure. Exit out of the Task Manager.
2] Goto Start > Run, type in msconfig (to be clear that is MSCONFIG), and click OK. In the new window go to the Startup tab and look down the list for any MyStart and/or Incredibar entries. If you find any, remove the tick then click Apply/OK. These changes will not take place until you next reboot the system.
3] Open Firefox and in the address bar type about:config . Accept the warning. When the list populates, type into the address bar MyStart and see what entries are found. Do the same for Incredibar. If entries are found, you can try and change those to default, but if you are not sure, copy the entries and post them into your reply here.
If none of these work your next options looks like referring on to another forum at BleepingComputer. To see what I mean, have a read of the discussion in the link below to see what steps had to be taken;
If you do go there, you would be best to register an account and post your question to get personal help from them.