How do I get Safari to recognize changed keyboard shortcuts?

I am trying to setup a simple, memorable keyboard shortcut for switching between tabs (a useful feature that I wish Safari made easier). I wanted to do option+arrow key. So I sent to System Preferences>Keyboard>Keyboard Shortcuts and created the shortcut.

The new shortcut shows up in Safari when I drop down the Window menu, but the shortcut doesn't actually work. When I hit option+L or R arrow key, the window does not switch to the next or previous tab.

I even went back to Keyboard Shorcuts in System Preferences and created another "All Applications" shortcut with the same command. It still doesn't work.

Any thoughts? Has anyone successfully changed the "Select Next Tab" or "Select Previous Tab" commands in Safari?

Thanks!