Yes. Google Play Movies & TV has shipped with Lovefield for more than a year as of September 2015.
No. Lovefield is built from scratch.
Yes. Lovefield is designed to work with existing JavaScript libraries/frameworks from the very beginning. The Lovefield team is not omniscient nor omnipotent to give the answers for interoperability of specific library/framework you had, however, just assume yes, give it a try, and let us know if it does not work.
Check our performance dashboard. Details of benchmark is provided here. Your mileage can vary depending on the platform and browser you use, the best way to verify is to run the benchmark yourself on your target platform and browser.
Lovefield has relational query engine built-in, similar to SQLite, MySQL, or other relational databases. The difference is that Lovefield does not accept raw SQL statements; instead, it has a builder-pattern API to build queries.
Lovefield executes queries inside your browser. For more details, checkout this video or our design doc.
Lovefield uses those data stores to persist data, and is designed to work with different data stores such as IndexedDB and Firebase.
WebSQL is also used as a pure data store. Lovefield does not use WebSQL for indices or query execution.
As of October, 2015, tests show that Lovefield's IndexedDB backstore could not be run on Safari 8 or Safari 9 beta. Safari simply throws mysterious DOM errors that do not happen on IE, Firefox and Chrome. This has been reported to WebKit/Apple but there's no word about ETA of fix. Please specify your connect options to WebSQL or Memory as mentioned here.
That is true. Safari does not support any storage in private browsing, so WebSQL is not an option here. You may consider using Memory when detected private browsing in Safari.
For Firefox, see here.
Lovefield offers relational query with SQL-like syntax, which IndexedDB and Firebase don't.
WebSQL is considered obsolete and does not work cross-browser. Lovefield works cross-browser.