Move the Firefox sidebar to the right

First you have to find userChrome.css file. This file is located in your profile folder:

C:\Documents and Settings\your profile\Application Data\Mozilla

Now open userChrome-example.css and enter these lines:

/* Display the sidebar in opposite side */
#browser {
-moz-box-direction: reverse;
}

Finally Save that file as userChrome.css and close it.