firefoxkeyboard shortcutsmacmacossafari
Two things I miss from Firefox and Chrome when using Safari on Mac are the Command + Option + Arrows, that are replaced by Control + Tab or Command + Shift + Arrows, and specially the Command + #number, which will invoke bookmarks instead of tabs.
So I want to gather up ideas here on how to fix this. I've already found some on google, but I wish they were simpler – there could be a way to automate the setup.
edit: And that it wouldn't need a background app runnning.
The Gleebox extension for Firefox, Chrome and Safari is another alternative that I've just started experimenting with:
gleeBox is an experimental project that takes a keyboard-centric approach to navigating the web. It provides alternatives to actions that are traditionally performed via the mouse. Some of these are radically more efficient than using a mouse, some not so much. In all cases, they are mostly meant for keyboard and command line lovers
I've been using it in Chrome for a short period, and so far I've liked what I've seen.
If you use all three of the above browsers regularly, then it has the additional advantage of providing the same mechanisms across all of them.
I would suggest avoiding the issue altogether by preventing video/music from automatically playing. Here are three things you can do (together or separately) to help prevent auto playing video/sound.
Install AdBlock Plus, which will block most advertisements including those that automatically start playing video/sound.
Go to about:config and set media.autoplay.enabled to false. This supposedly stops HTML5 media from autoplaying, though I couldn't find any references to it in the about:config entries on MozillaZine Knowledge Base.
Go to about:config and set plugins.click_to_play to true. As you can see, it stopped Youtube from auto-playing this annoying video. 
Best Answer
Disclaimer
Actually, there is generic answer from @donut -- thanks for this contribution! However, it wasn't clear from me when I met it. Thus, let me to concrete it exactly for Command + Option + Left/Right as it was asked initially.
Solution for using Command + Option + Left/Right in Safari
Solution for using Command + 1, 2, 3... in Safari