it will test transactions that are in 3 different states:

• transaction has received some data before the protocol error occurred. This transaction will be closed with NS_ERROR_NET_PARTIAL_TRANSFER
• transaction has only send some data but has not received any data. This transaction will be closed with NS_ERROR_NET_HTTP3_PROTOCOL_ERROR
• transaction is queued in Http3Session because of the stream concurrency limit. In this case the transaction will be restarted and it will succeeed using HTTP2.

https://treeherder.mozilla.org/jobs?repo=try&revision=673ce4bc6f6c46003af25eee2992b1218e8370b5

Backed out for failures on test_http3_fatal_stream_error_2.js

backout: https://hg.mozilla.org/integration/autoland/rev/efd7c9b709cd336043641adbd6bed8f83e65a2fe

push: https://treeherder.mozilla.org/jobs?repo=autoland&selectedTaskRun=NGi-CcZFSb2Md9GbGaR6nQ.0&revision=7c4261286c2389349ff2e27ae2ac8cb6bed46d83

failure log: https://treeherder.mozilla.org/logviewer?job_id=321521364&repo=autoland&lineNumber=3223

[task 2020-11-12T01:47:05.918Z] 01:47:05 INFO - TEST-START | netwerk/test/unit/test_http3_fatal_stream_error_2.js
[task 2020-11-12T01:47:07.561Z] 01:47:07 WARNING - TEST-UNEXPECTED-FAIL | netwerk/test/unit/test_http3_fatal_stream_error_2.js | xpcshell return code: 0
[task 2020-11-12T01:47:07.561Z] 01:47:07 INFO - TEST-INFO took 1650ms
[task 2020-11-12T01:47:07.561Z] 01:47:07 INFO - >>>>>>>
[task 2020-11-12T01:47:07.562Z] 01:47:07 INFO - PID 15693 | Couldn't convert chrome URL: chrome://branding/locale/brand.properties
[task 2020-11-12T01:47:07.563Z] 01:47:07 INFO - PID 15693 | [15693, Main Thread] WARNING: Couldn't get the user appdata directory. Crash events may not be produced.: file /builds/worker/checkouts/gecko/toolkit/crashreporter/nsExceptionHandler.cpp:2949
[task 2020-11-12T01:47:07.563Z] 01:47:07 INFO - (xpcshell/head.js) | test MAIN run_test pending (1)
[task 2020-11-12T01:47:07.564Z] 01:47:07 INFO - (xpcshell/head.js) | test run_next_test 0 pending (2)
[task 2020-11-12T01:47:07.564Z] 01:47:07 INFO - (xpcshell/head.js) | test MAIN run_test finished (2)
[task 2020-11-12T01:47:07.564Z] 01:47:07 INFO - running event loop
[task 2020-11-12T01:47:07.565Z] 01:47:07 INFO - PID 15693 | [15693, Main Thread] WARNING: Could not get the program name for a cubeb stream.: 'NS_SUCCEEDED(rv)', file /builds/worker/checkouts/gecko/dom/media/CubebUtils.cpp:380
[task 2020-11-12T01:47:07.565Z] 01:47:07 INFO - netwerk/test/unit/test_http3_fatal_stream_error_2.js | Starting setup
[task 2020-11-12T01:47:07.565Z] 01:47:07 INFO - (xpcshell/head.js) | test setup pending (2)
[task 2020-11-12T01:47:07.565Z] 01:47:07 INFO - TEST-PASS | netwerk/test/unit/test_http3_fatal_stream_error_2.js | setup - [setup : 29] "47448" != null

There are some r+ patches which didn't land and no activity in this bug for 2 weeks.
:dragana, could you have a look please?
For more information, please visit auto_nag documentation.

I will not have time to work on this bug, so I am unassigning myself.