Note: For this tweak I recommend using the ChromEdit Plus extension.
The Firefox sidebar can display bookmarks, history and other content. Some users may prefer to have the sidebar displayed on the right side of the screen instead of the left. Simply add these lines to your userChrome.css file located in your profile folder:
/* Display the sidebar in opposite side */
#browser {
-moz-box-direction: reverse;
}When you are done editing your userChrome.css file, close and restart Firefox and the changes should take effect right away.
Source:Mozilla Links
It helped me out.
Thanks.
Guys maybe something for Firefox 5?) Because it did not work for me
It still works in Firefox 5. Make sure you close Firefox before making changes to the userChrome.css or use the ChromEdit Plus add-on.