Try to rearrange extensions in extensions.ini file - in my case it helped to place "Google Toolbar" over "Web Developer" toolbar.
Location of file:
You have to change the numbered order, not just drag your preferred entry to the top of the list.
At the start of each line you'll see, respectively 'Extension0' then 'Extension1' etc. Change that final digit as required. Not all Extensions generate a Toolbar, of course, so in some instances the order may be irrelevant. I just made my Google toolbar '0', so I hope it'll always appear at the top.
I originally thought the physical order in the file was not important, but when I rebooted the computer and re-opened FF I found the extensions had re-ordered themselves. So now I've BOTH changed the numbering AND dragged them into the new order. I'm hoping this will work permanently. I'm working with FF14.