Infinite spinning in Firefox

[halmai]

After opening the page, I click the [CREATE ENDPOINT] button. It starts to spin and never stops.

The console shows the error message:

IDB::Error
kernel.js:674:21
DOMException
​
code: 0
​
columnNumber: 0
​
data: null
​
filename: ""
​
lineNumber: 0
​
message: "The operation failed for reasons unrelated to the database itself and not covered by any other error code."
​
name: "UnknownError"
​
result: 2154168321
​
stack: ""
​
__proto__: DOMExceptionPrototype { name: Getter, message: Getter, INDEX_SIZE_ERR: 1, … }

Details: FF version 60.0b16 (64-bit), running on MacOSX El Captain version 10.11.6 (15G1212)