I often use a simple (button image) link to twitter.com/share or facebook.com/sharer.php (now http://developers.facebook.com/docs/reference/dialogs/). That is one-click without javascript execution or, worse IMO, company custom html tags.

AFAIK Google+1 doesn't, as of yet, have such an URL where you can share. Sharing seems to go through the +1 button. I'd really like a share url for Google+ for technical and privacy reasons and keep everything one-click to share.

I bet you could make a two-click system for the Google+1 button, now asynchronous javaScript loading is enabled, but I don't know if that is within TOS. Again I would love a simple share link (like Linkedin, Facebook or Twitter) and be done with it.

I know that sharing on Facebook is different from liking, but I feel sharing is more valuable from a marketing POV.

For Firefox there's an add-on, take a look:

https://addons.mozilla.org/en-US/firefox/addon/2-click-like/

It supports five or six like buttons.