Updates and Fixes

[kennethkutyn-optimizely]

Found and fixed a couple issues:

1. Need to wait for body before trying to add extension
2. Need to check if extension exists before attempting to remove
3. Default value for selector was not one of the options.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}