I had the same problem but found a way round it. You have to install this extension called userChrome.js . Download and install it from here:
http://mozilla.zeniko.ch/userchrome.js.html
Now restart your browser as it asks you to, and go to "My Computer".
Go to:
"C:\Documents and Settings\(your computer user name)\Application Data\Mozilla\Firefox\Profiles\"
and there may be more than 1 folder. Find the one that has a folder called "chrome" inside. Open the chrome folder and minimize it.
Now download the attached ".zip" file, and unzip it. Inside you should find a file called "userChrome.js". Copy or move this file to the "chrome" folder you have minimized, and it will say the same file name already exists. Just press replace.
Close the folder, and restart your firefox browser. Click on your bookmarks with either a left click or middle button, and it will go to the next tab.
This worked perfect for me, and I am sure it will work for you too. I have saved you the trouble of adding codes and scripts, by attaching the finished file. I hope it helps.
As an extra thing, if you enjoy using tabs and would like to manage your tabs better download Tab Mix Plus. This just enables you to customise them with where the tabs are and what colour etc. You can find that here:
http://tmp.garyr.net/tab_mix_plus-dev-build.xpi
Hope this info helps mate
Ihsan || Kai
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Just realised mate you are using OSX. Here is the folder you should be going to, to find the "chrome" folder:
/Macintosh HD/Users/<username>/Library/Mozilla/Firefox/Profiles/
AND
/Macintosh HD/Users/<username>/Library/Application Support/Firefox/Profiles/
In these folders you may find more than one folder inside. Just look for the one with the "chrome" folder, and move the attached file to that.
Hope it works, because I only tested on XP. It should work.....