Many aspects of Firefox's interface can be modified by applying custom style rules. Once you know the rules you want to use, you can apply them using either the Stylish extension or by creating/editing a userChrome.css file. Personally I prefer Stylish for easy tweaking and previewing, but if you don't want any more extensions, then userChrome.css would be the approach for you.

Anyway, assuming you do not use the top of the browser for either the Title Bar or the Menu bar, then this pair of rules will slide the buttons to the left for you:

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
/* Suppress the spacer that keeps the min/max/close buttons on the right */
#titlebar-spacer {
    display:none !important;
}
/* Adjust the margins so the buttons do not overlap the tabs */
#titlebar-buttonbox-container {
    margin-top: -8px !important;
    margin-bottom: 10px !important;
}

You can see the result in the attached screen shot.

However, this doesn't work with the Title Bar or Menu bar, and the buttons are half obscured when the window is maximized, so it definitely needs more work.

If you search around, perhaps someone already has posted a more complete solution.

Nope. It didn't work, ive also already searched :(

Hmm, it worked on a "Basic" Windows 7 theme, but I can't see a way to move the buttons on an "Aero" theme.

For some reason it works on pale moon but not firefox, see next post

Firefox pic