With the following extension, you can change the order:

• https://addons.mozilla.org/en-US/firefox/addon/menu-editor/

You need to update the following. The Plugin version(s) shown below was/were submitted with your question and is/are out of date. You should update to avoid known security issues with the version(s) you have installed. Click on "More system info..." to the right of your question to see what was included with your question.

• Adobe PDF Plug-In For Firefox and Netscape 8.3.0 (Very old. You may need to remove in Windows Control Panel > Add or Remove Programs)
• Shockwave Flash 10.3 r181 (may be current; in Add-ons > Plugins the most current version is 10.3.181.26)

1. Check your plugin versions on either of the following links':
   • http://www.mozilla.com/en-US/plugincheck/
   • https://www-trunk.stage.mozilla.com/en-US/plugincheck/
   • Note: plugin check page does not have information on all plugin versions
   • There are plugin specific testing links available from this page:
     • http://kb.mozillazine.org/Testing_plugins
2. Update Adobe Reader (PDF plugin):
   • From within your existing Adobe Reader (if you have it already installed):
     • Open the Adobe Reader program from your Programs list
     • Click Help > Check for Updates
     • Follow the prompts for updating
     • If this method works for you, skip the "Download complete installer" section below and proceed to "After the installation" below
   • Download complete installer (if you do NOT have Adobe Reader installed):
     • SAVE the installer to your hard drive (save to your Desktop so that you can find it after the download). Exit/Close Firefox. Run the installer you just downloaded.
     • Use either of the links below:
       • https://support.mozilla.com/en-US/kb/Using+the+Adobe+Reader+plugin+with+Firefox (click on "Installing and updating Adobe Reader")
       • Also see Download link': http://get.adobe.com/reader/otherversions/
   • After the installation, start Firefox and check your version again.
3. Update the Flash plugin to the latest version.
   • Download and SAVE to your Desktop so you can find the installer later
   • If you do not have the current version, click on the "Player Download Center" link on the "Download and information" or "Download Manual installers" below
   • After download is complete, exit Firefox
   • Click on the installer you just downloaded and install
     • Windows 7 and Vista: may need to right-click the installer and choose "Run as Administrator"
   • Start Firefox and check your version again or test the installation by going back to the download link below
   • Download and information: http://www.adobe.com/software/flash/about/
     • Use Firefox to go to the above site to update the Firefox plugin (will also install plugin for most other browsers; except IE)
     • Use IE to go to the above site to update the IE ActiveX
   • Download Manual installers.
     • http://kb2.adobe.com/cps/191/tn_19166.html#main_ManualInstaller
     • Note separate links for:
       • Plugin for Firefox and most other browsers
       • ActiveX for IE

You can also do this with code in userChrome.css

See my post here: /questions/791244?page=2#answer-161497

Just discovered this that may help. I use Tab Mix Plus, my favorite add-on. The first page gives you the option, in a check box, to use Single Window Mode. In that case, you will not have the option in the drop down window to open a new window. If you UNCHECK single mode window, the dropdown menu first item is to open in a new Window.

My problem is the opposite of the OP, but the result is the same. Years of using earlier versions of Firefox have conditioned me to open links in a new tab by selecting the second right-click menu choice without looking. After a week of trying to readjust to the reversed locations of "open link in new window" and "open link in new tab", I'm still unintentionally opening new windows instead of tabs time after time after time. The point is, why should I have to adjust ( or need an external plugin to fix your problem). YOU TAUGHT ME HOW TO DO IT THIS WAY, so why did you change it? Do you think the reversal is more efficient? Did some study group of new users pick the new lineup? Did you have a taste test with Pepsi? Have you adopted Microsoft's "we know what you want better than you do" policy? People in England drive on the left side of the road with the steering wheel on the right. Maybe that's actually a better way of doing it. Maybe we should just re-engineer all new american model cars that way and reverse all the traffic signs overnight without any warning -- no announcements, no choice, just do it because the engineers decide it's better. While we're at it, maybe you should adopt MS's "Ribbon" menu next. Do I sound a little angry or as if I have too much time on my hands? If so, that's because I am and I don't have enough to relearn the same tasks every time you think of a better way to perform a basic operation. I'm sick of perfectly workable programs being "improved" in ways that offer no improvement, only the necessity of retraining.