Been chasing my tail with this today & am reluctantly admitting defeat.
I'm assuming from the fact that I keep opening bookmarks from firefox 29.0.1 toolbar over the existing tab that the order has changed from the previous version, so that 'Open' is now the top option & previously wasn't. Unless I'm imagining things.
I've found any amount of articles on how to do related stuff (such as change context menu order for opening links, removing items from other menus), but don't seem able to track down this exact thing.
I've created the userChrome.css file and have been trying out stuff with that, I just need the right code for changing the order of the menu to 'Open in New Tab' at top, or alternatively hiding Open altogether. Assuming it's possible & I don't see why it shouldn't be.
I know I can just middle click but now I'd just like to know how to do it this way.. & also how I could have gone about finding it myself. Thanks .
/edit
sorted with the aid of this https://groups.google.com/forum/m/#!...ox/xNs6dBmpKZc (the only article I've found so far that covered opening bookmarks, rather than the behaviour of bookmarks folders or bookmarks menu) & a bit of fiddling around.