`wasm-pack test --headless --firefox` fails

[ordian]

🐛 Bug description

wasm-pack test --headless --firefox fails to run while wasm-pack test --headless --chrome works

🤔 Expected Behavior

Tests run with firefox.

👟 Steps to reproduce

❯ git clone https://github.com/paritytech/parity-common
❯ cd parity-common/kvdb-web 
❯ wasm-pack test --headless --firefox         
[INFO]: Checking for the Wasm target...
    Finished dev [unoptimized + debuginfo] target(s) in 0.05s
[INFO]: Installing wasm-bindgen...
    Finished test [unoptimized + debuginfo] target(s) in 0.05s
     Running /path/to/parity-common/target/wasm32-unknown-unknown/debug/deps/kvdb_web-37ead5ffc7c62ce0.wasm
no tests to run!
     Running /path/to/parity-common/target/wasm32-unknown-unknown/debug/deps/indexed_db-efc9b9a79c4c3fbe.wasm
Set timeout to 20 seconds...
Running headless tests in Firefox on `http://127.0.0.1:39353/`
Try find `webdriver.json` for configure browser's capabilities:
Not found
driver status: signal: 9                          
driver stdout:
    1596449767193   geckodriver INFO    Listening on 127.0.0.1:39353
Error: non-200 response code: 500                 
{"value":{"error":"unknown error","message":"Invalid Content-Type","stacktrace":""}}
error: test failed, to rerun pass '--test indexed_db'
Error: Running Wasm tests with wasm-bindgen-test failed
Caused by: failed to execute `cargo test`: exited with exit code: 1
  full command: "cargo" "test" "--target" "wasm32-unknown-unknown"

🌍 Your environment

OS: GNU/Linux wasm-pack version: 0.9.1 rustc version: 1.45.1 stable

[chinedufn]

The problem is https://github.com/rustwasm/wasm-bindgen/issues/2261

[ordian]

The problem is rustwasm/wasm-bindgen#2261

Thanks for the link! So this is a bug in geckodriver 0.27?