Type about:config in the address bar and filter by 'search' and double click on the key shown below.
Just a quick note: Taking screenshots on Linux (Ubuntu for me) doesn't work the same as in Windows. In Windows, you just need to do PrtScrn or Alt-PrtScrn and ctrl-v (paste) into the blog post. Under Ubuntu, I have to PrtScrn or Alt-PrtScrn and I get a dialog box to save my screenshot to the desktop. I can't then drag-and-drop the picture into the blog post but have to invoke the Flock photouploader to get the picture into the photobar and then drag it into the blog post.