How to change FireFox switch tab shortcut on OS X?

updated for macOS and current Firefox.

1. default shortcut: Command+Option+⭠ and Command+Option+⭢
2. alternative shortcut: Ctrl+Tab and Ctrl+Shift+Tab
   this shows firefox tab switcher in current version
3. alternative shortcut: Command+{ and Command+}
   this actually requires 3 keys to be pressed on US keyboard Command+Shift+{ and Command+Shift+} and may not work with other keyboard languages
4. alternative shortcut: Ctrl+Page Up and Ctrl+Page Down
5. you can also jump to tabs directly with Cmd+1, Cmd+2, Cmd+3, Cmd+4 etc.
6. you can try a Firefox add-on focused on switching tabs which suits your needs: Add-ons browser
7. just use a BetterTouchTool to remap any keystroke or mouse/trackpad gesture you want to already existing Command+Option+⭠ and Command+Option+⭢ keystrokes.

I personally prefer #7: Command+Option+⭠ and Command+Option+⭢ for switching tabs. I haven't modified Firefox at all and I used BetterTouchTool to remap keystrokes in every other app which uses other commands that these two. Now I can use Cmd+Option+⭠ and Command+Option+⭢ to switch tabs across all apps I use on Mac and it works great.