There are prefs that set the mousewheel action for various modifiers. You can modify the delta_multiplier_y pref for a specific modifier to a lower value to scroll less and set its action to '1' to scroll.

Mousewheel prefs:

• mousewheel.default.action
• mousewheel.with_*.action
• mousewheel.with_alt.action = 2
• mousewheel.with_control.action = 3
• mousewheel.with_meta.action = 1
• mousewheel.with_shift.action = 4
• mousewheel.with_win.action= 1

Action:

0: Nothing happens
1: Scrolling contents
2: Go back or go forward, in your history
3: Zoom in or out (reflowing zoom)
4: Treat vertical wheel as horizontal scroll
5: Zoom in or out (pinch zoom)

There are prefs that set the mousewheel action for various modifiers. You can modify the delta_multiplier_y pref for a specific modifier to a lower value to scroll less and set its action to '1' to scroll. Mousewheel prefs:

• mousewheel.default.action
• mousewheel.with_*.action
• mousewheel.with_alt.action = 2
• mousewheel.with_control.action = 3
• mousewheel.with_meta.action = 1
• mousewheel.with_shift.action = 4
• mousewheel.with_win.action= 1

Action: 0: Nothing happens 1: Scrolling contents 2: Go back or go forward, in your history 3: Zoom in or out (reflowing zoom) 4: Treat vertical wheel as horizontal scroll 5: Zoom in or out (pinch zoom)

I don't want mousewheel I want arrow up/down +alt to scroll like it's in chrome.

Ok I adjusted this toolkit.scrollbox.verticalScrollDistance from 3 to 40 so I just press arrow up/down it scrolls more.