Hls.js: TextTrack won't clear when seeking in FireFox

[shalommeoded]

What version of Hls.js are you using?

12.4

What browser and OS are you using?

MacOS (High Sierra) and Windows 10 (64-bit), FireFox 67.0 (64-bit)

Test stream:

https://hls-js.netlify.com/demo/?src=https%3A%2F%2Fd2zihajmogu5jn.cloudfront.net%2Fbipbop-advanced%2Fbipbop_16x9_variant.m3u8&demoConfig=eyJlbmFibGVTdHJlYW1pbmciOnRydWUsImF1dG9SZWNvdmVyRXJyb3IiOnRydWUsImVuYWJsZVdvcmtlciI6dHJ1ZSwiZHVtcGZNUDQiOmZhbHNlLCJsZXZlbENhcHBpbmciOi0xLCJsaW1pdE1ldHJpY3MiOi0xLCJ3aWRldmluZUxpY2Vuc2VVcmwiOiIifQ==

Checklist

• [X] The issue observed is not already reported by searching on Github under https://github.com/video-dev/hls.js/issues
• [X] The issue occurs in the stable client on https://hls-js.netlify.com/demo and not just on my page
  
• [X] The issue occurs in the latest client on https://hls-js-latest.netlify.com/demo and not just on my page
  
• [X] The stream has correct Access-Control-Allow-Origin headers (CORS)
• [X] There are no network errors such as 404s in the browser console when trying to play the stream

Steps to reproduce

1. Open https://hls-js.netlify.com/demo in FireFox.
2. Test with the stream in the above.
3. When seeking back or forth, the captions are getting stuck on the textTrack and would not
   clear.

Expected behavior

The textTrack should dispaly only the correct VTTCue.

Actual behavior

VTTCues are getting stuck on the textTrack and would not clear.

See screenshot:

[johnBartos]

@shalommeoded Thanks for the report, I'll schedule this for the next minor patch.

[OrenMe]

this is a reported Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1551285
It is fixed on Firefox 68.

[johnBartos]

@OrenMe Great, thanks for looking into this. Can confirmed its fixed