UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Firefox/52.0

Steps to reproduce the problem:
1. Open https://jsfiddle.net/pehrsons/a9gugbut/
2. Hit start

What is the expected behavior?
You should only get a "dataavailable" event after clicking on Stop.

What went wrong?
There are many "dataavailable" events without any timeslice is set.

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 55.0.2883.95 (Official Build) (64-bit)  Channel: stable
OS Version: OS X 10.12
Flash Version: 24.0.0.186

The spec reads under the start method:

If timeslice is not undefined, then once a minimum of timeslice milliseconds of data have been collected, or some minimum time slice imposed by the UA, whichever is greater, start gathering data into a a new Blob blob, and queue a task, using the DOM manipulation task source, that fires a blob event named dataavailable at target with blob. Note that an undefined value of timeslice will be understood as the largest long value.

---

I.e., when no timeslice is passed it's understood as the largest long value (let's call it MAX). Whichever is greater between an internal UA minimum time slice and MAX is always MAX. Hence only after MAX milliseconds have passed should data be gathered into a blob. You are currently breaking the spec.

Note that in Firefox we switch to caching the data in a temporary file on disk when the recorded data grows too large.