Linux: Firefox exposes reserved Xbox Series buttons and swaps X/Y

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#83 opened on Aug 15, 2026 0 comments 0 reactions 1 assignee View on GitHub

@LizardByte-bot is already working on this.

Since Aug 15, 2026.

Assessment

This issue has not been assessed yet.

Description

Environment

Host OS: Linux
Virtual controller provider: libvirtualhid through Sunshine
Profile: Xbox Series
Browser: Firefox
Reported identity: 045e-0b13-Sunshine (libvirtualhid) X-Box Series Controller
Tester: https://app.lizardbyte.dev/gamepad-tester/

Observed behavior

Firefox exposes 20 buttons.
B17 is the Share button and is now labeled correctly by gamepad-helper.
B18 and B19 remain visible but do not represent real Xbox Series controls.
The physical X and Y buttons are swapped.
Chromium exposes only B17 beyond the standard buttons and reports X/Y correctly.

Source-level explanation

The Linux uinput backend advertises KEY_RECORD for Share and also advertises reserved BTN_C and BTN_Z capabilities to preserve sparse Xbox button slots. Firefox starts with 17 canonical buttons and then appends every advertised nonstandard key capability, producing:

B17: KEY_RECORD
B18: reserved BTN_C
B19: reserved BTN_Z

Firefox only applies its Xbox-specific BTN_NORTH/BTN_WEST correction when an ancestor driver is named xpad or microsoft. A uinput-created virtual controller does not have either driver ancestry despite using Microsoft VID/PID.

Firefox source:
https://searchfox.org/firefox-main/source/dom/gamepad/linux/LinuxGamepad.cpp

Expected behavior

Firefox exposes the standard 17 buttons plus Share at B17.
No phantom B18/B19 controls are presented.
X and Y match the physical Xbox layout.

Constraints

Steam currently handles this virtual Xbox Series controller correctly and is the priority consumer. Do not remove reserved capabilities or swap emitted X/Y without validating Steam and Chromium. Keep any compatibility change Linux-specific and avoid changing the Windows backend.

Dominant language: C++
Stars: 57
Forks: 15
Avg merge: 10h 54m
Merged PRs (30d): 32

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