Thanks for your 1-star review. Setting your homepage to SearchScene is one of the stated features of the extension. This is in order to give you beautiful scenery when you first open your browser and easy access to the SearchScene search box. From the extension description...
"By adding this extension, you make SearchScene:
- your homepage and start page
- your new tab
- your default search engine."

If you wish to just make SearchScene your default search engine (and leave your homepage and new tab unchanged) we also have an extension that sets SearchScene as your default search engine only...
https://addons.mozilla.org/en-GB/firefox/addon/searchscene-default-search/