I use Neater Bookmarks for Chrome. And you get something akin to a sidebar (more like a vertical drop-down menu, but with nice space for helping to organize bookmarks. I find it to be a very useful extension.
There's a picture of what you get at that link. To use a Chrome extension in Opera, you need the Opera Extension, called "Download Chrome Extension." https://addons.opera.com/en/extensions/?ref=menu
The Gmail info in http://operawiki.info/WebMailto should still work. Just set it after you upgrade to 12.17 if you're using 12.16.
If you're using Opera 20, you can just use the Gmail Compose Extension. Or, if you're using Opera 12, the older versions of the extension (1.7 for example) are here.
The extension doesn't handle mailto URIs typed into the address field though. It only handles links on web pages (due to Opera not offering enough power to extensions).
Go back to the topic list. At the top of the page it says "All Discusions" "My Discussions" ... and if you have a saved draft it should also say Drafts. Click on that. (You can also get to it from your profile.)
Page loading is how long a webpage takes to fully display all text, images and so on. This is sometimes referred to as >"drawing". You can set your preference for how soon Opera should attempt to display a page after it starts loading.
I think that my extention isn't compatible. I installed Download Chrome Extension and Dropmark sidebar. When installing Dropmarks I got a yellow bar at the top of the browser, I forgot what it said , and when taken to my extentions page, checking if it's enabled, and clicking Extention keyboard shortcuts I got this.