MacOS – Use custom App Shortcuts: Find “Menu Command” for Chrome switch to right/left Tab

You can use KeyRemap4MacBook to for example turn the right option into an extra modifier key for opening applications:

<?xml version="1.0"?>
<root>
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_FINDER</name>
    <url>file:///System/Library/CoreServices/Finder.app</url>
  </vkopenurldef>
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_SAFARI</name>
    <url>file:///Applications/Safari.app</url>
  </vkopenurldef>
  <item>
    <name>test</name>
    <identifier>test</identifier>
    <autogen>__KeyToKey__ KeyCode::OPTION_R, KeyCode::VK_MODIFIER_EXTRA1</autogen>
    <autogen>__KeyToKey__ KeyCode::F, ModifierFlag::EXTRA1, KeyCode::VK_OPEN_URL_FINDER</autogen>
    <autogen>__KeyToKey__ KeyCode::S, ModifierFlag::EXTRA1, KeyCode::VK_OPEN_URL_SAFARI</autogen>
  </item>
</root>

See http://osxnotes.net/keyremap4macbook.html for more examples.

If you have bought the Powerpack for Alfred 2, you can use workflows like this:

Hotkeys have a short delay by default, but you can reduce it by changing the trigger behavior:

You can install Google Chrome and use it side by side with other browsers such as Safari (built-in), Firefox (need to download & install), and Opera (need to download & install).

One of the browsers will need to be set as your default. This can be changed in System Preferences > General.

It's worth noting, Safari is the default browser in all versions of OS X and iOS. Google Chrome is also a browser, and Yosemite is an operating system. Your question is a bit misguided. You don't necessarily "switch between Google Chrome and Yosemite". That said, if you're talking about editing a website via online tools through web hosting providers such as Squarespace, presuming they support Chrome they'll also likely support Safari. I'd suggest first trying to update the site in Safari before you download and install a browser which you may not even need.