Unexpected modifier key (Fn) behaviour with some trackpad gestures?

Bugs or Unexpected Behavior
1

Hi there,

I’m experiencing an issue with certain simple trackpad gestures triggering modifier key behaviour (function / Fn) in Chrome/Firefox.

As I use the Fn key for voice dictation (using Willow Voice), this disrupts my workflow and is a general annoyance. No other gestures trigger this behaviour, from my tests.

Observe the behaviour below.

Zight Recording 2026-05-05 at 01.06.29 pm

First, I show my BTT configuration for these two gestures.

Second, I trigger the two BTT gestures (3 finger swipe left/right) — both cause voice dictation to activate, as if the Fn key was pressed down.

Third, I trigger the actual raw, underlying keyboard shortcuts (Option + Command + ← for Select Previous Tab; Option + Command + → for Select Next Tab). These work as intended, and does not trigger modifying key behaviour.

Please let me know if you need additional information, e.g. debug logs.

Would love to see this fixed!

Device information:

  • Type of Mac: MacBook Pro 14” — 2021 (MacBookPro18,3 / MKGT3B/A)
  • macOS version: 15.7.4
  • BetterTouchTool version: 6.477
2

arrow keys implicitly contain the FN key on macOS. Maybe the app you are using doesn't correctly differentiate these for programmatically generated key presses. Unfortunately I don't think I can fix this on BTT's side

3

Thanks for the response (and for building one of my favourite apps), Andreas!

Question: why is it that when I press the keyboard shortcut normally (for example, ⌥ + ⌘ + ←), it doesn't trigger the FN key behaviour? It seems to only be when I use the trackpad gesture.

I will also reach out to the creators of Willow Voice for their ideas on a solution.

4

Unfortunately non-programmatic events are slightly different. I'll check out willow voice and see whether I can figure out a way to prevent this!

5

For now, maybe use the predefined action "Trigger Menubar Menu Item" instead of the shortcuts. These should prevent the issue

6

That works!! Thank you Andreas — solved :yellow_heart: