Yes. CircuitBlocks saves as you work, and projects are stored in your CircuitBlocks account rather than in the browser.
Automatic saving
Each time you add or change a block, the editor writes the change. If a tab closes or the power goes, the last saved change is there when you sign back in.
Where projects are stored
Projects are kept on our servers, not in local browser storage, so they do not depend on one browser's temporary files.
Saving by hand
You can also save at any point with the save icon in the top-left corner of the project editor.
There is no export
Because projects are stored on the server, there is no export feature and they cannot be downloaded as files. You reach them by signing in to your CircuitBlocks account.