Currently, a fresh installed JabRef has fulltextsearch option enabled.
Suggestion: Set the default option to deactivated

Explanation:

1. The fulltextsearch option does not seem to be documented in the help files (https://docs.jabref.org/finding-sorting-and-cleaning-entries/search)
2. The fulltextsearch option indexes and searches files beyond the core program and the loaded libraries. A standard setting that is confined to the core of the program is way more intuitive.
3. Searching a large library takes some time and makes the program unresponsive for a short period. Users who are not aware of the feature might think the program is just slow. This happend to me as a long time user of JabRef. I am still stuck at 4.3. due to performance issues in previous versions. After trying the most recent 5.8 I thought there are still perfomance issues, because searching took way to long for my database. I simply was not aware, that the attached files are search as well.