Rebinding next/previous tab in Firefox without a plugin - firefox

Question

I use a tool called Autokey on Linux so that I can bind next/previous tab to the hotkeys that I want across all applications. For the most part, the built in OSX key mapper does the job when I need to use a mac. The problem is that it can only trigger actions that appear as a menu item in an application and Firefox doesn't actually have a 'Next tab' or 'Previous tab' menu item like Chrome does.
I'd rather not install a Firefox plugin just to keybind certain functionality. They always end up messing me up on other operations systems or getting outdated. Is it possible to create an extension that contributes menu items to Firefox so I can just use the built in keyboard shortcut utility in OSX? Are there other ways of getting the keybinds I want?

Answer 1

I ended up solving this with Karabiner in a way that is more analogous to how Autokey works. Here is the json config that maps my preferred next/previous keybind to the thing Firefox (and iTerm) needs.
{
"global": {
"check_for_updates_on_startup": true,
"show_in_menu_bar": true,
"show_profile_name_in_menu_bar": false
},
"profiles": [
{
"complex_modifications": {
"parameters": {
"basic.simultaneous_threshold_milliseconds": 50,
"basic.to_delayed_action_delay_milliseconds": 500,
"basic.to_if_alone_timeout_milliseconds": 250,
"basic.to_if_held_down_threshold_milliseconds": 500,
"mouse_motion_to_scroll.speed": 100
},
"rules": [
{
"manipulators": [
{
"type": "basic",
"description": "next tab in firefox",
"from": {
"key_code": "l",
"modifiers": {
"mandatory": ["left_control", "left_gui"]
}
},
"to": [
{
"key_code": "tab",
"modifiers": ["left_control"]
}
],
"conditions": [
{
"type": "frontmost_application_if",
"bundle_identifiers": [
"org.mozilla.firefox",
"com.googlecode.iterm2"
]
}
]
},
{
"type": "basic",
"description": "prev tab in firefox",
"from": {
"key_code": "h",
"modifiers": {
"mandatory": ["left_control", "left_gui"]
}
},
"to": [
{
"key_code": "tab",
"modifiers": ["left_control", "left_shift"]
}
],
"conditions": [
{
"type": "frontmost_application_if",
"bundle_identifiers": [
"org.mozilla.firefox",
"com.googlecode.iterm2"
]
}
]
}
]
}
]
}
}
]
}
I use an Ergodox keyboard and the way I programmed it makes my left alt key appear as left_gui.