Involved but simple and may locate source file locations

Okay, I think I've got it.

1)In about:config, search "mystart" and "incredibar" and reset all values directly pertaining to those two terms.

2)search for "extensions.installCache" if you open the string and scroll carefully, you should see something that looks like the following:

'{"name":"app-profile","addons":{"ffxtlbr@incredibar.com":{"descriptor":"C:\\Users\\**YourUsername**\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\mq917j3n.default\\extensions\\ffxtlbr@incredibar.com"'

3) Follow this string to find the location of the MyStart addon. When you find the containing folder, in this case "ffxlbr@incredibar.com," DO NOT DELETE it, but take note of and rename all the files with non-executable extensions like ".jpg". ".com" is another form of executable and should be treated and renamed just like any suspicious ".exe" should. If you notice anything crashing or functioning improperly, you can simply rename the files with their original names, no harm done.

4) Redo all scans, and make sure you clean everything up as suggested by others, resetting values in Firefox, etc.

5) If you have no problems with any other extensions' performance after a week or two's use, go ahead and delete that containing folder if you feel it won't affect anything as these were likely your target files.

Happy Hunting, and I hope this works for you!
Devin