1) Via Bookmarklet: Drag Google Talk to your Bookmarks Bar for 1-click access to a floating version of Google Talk.
2) Into Firefox Sidebar: go to http://talkgadget.google.com/talkgadget/client, bookmark it, and check the "Load this bookmark in the Sidebar" checkbox in the dialog that pops up: Hit OK, click the bookmark, and it will open in Firefox's sidebar panel.
Done!, Give your Valuable Comments.

