Chrome
- Disable background sync for websites.
- Enable gmail sync but disable passwords.
- Enable enhanced spell checker.
⇧+Delete: delete the overlayed entry of the auto-complete fields history. ⇧+Fn+Delete: delete an entry from the auto-complete in the URL bar.
I particularly find really dangerous to accidentally press ⌘Q. A way to disable this is:
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Go to System Preferences > Keyboard > Shortcuts > App Shortcuts
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Application: Google Chrome.app
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Menu title: 'About Google Chrome' (or anything else you may want to open, this text represents the name of what you want to open from the app menu, the top bar)
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Key Shortcut: press ⌘Q.
You can also do this for example for ⌘⌥W that closes all the open tabs. I think in OS X you can't map two keyboard shortcuts to the same menu. So you can remap ⌘⌥W to 'Downloads', for example.