The D3300 was first supported in Lightroom 5.4.
The Mac version does not matter provided it's running the version of OS X you need to run Lightroom 5.5.
Check which version of Lightroom you are using.
In Lightroom, click Help > System Info and look at the first line in the white box (where it says Lightroom version:)
Currently I am running Lightroom 5.6 and Camera Raw 8.6.
I have read in previous posts regarding D3300 being supported in Lightroom 5.4 and Camera Raw 8.4. I tried installing new plugins, I tried downloading a nef to dng converter .. nothing.
I still don't understand why in the previous macbook pro model using the same version of lightroom and trying to open the same file everything works fine and why when i try to open the same photo in my mac it says that preview is unavailable.
I repeat I tested the same photo in two different computers using the same version of Lightroom (5.6) with Camera raw 8.6.
I'm not sure what you are doing.... so when you say you are trying to "open" are you meaning "import"????
If so from where to where and what is the exact message given??
yeap sorry for that ... I meant import.
As the new macbook does not have a card reader and I have just ordered one, I uploaded a picture to dropbox and downloaded in my mac.
So to reply to your question I try to import it from my desktop to Lightroom and I get the message "failed to find a place for the imported file".
Also the thumbnail says "preview unavailable for this file".
Ok so a little update
I have found a way to import my nef files but it is kind of weird and I cannot explain it.
When I route the photos directly from my Dropbox folder they can be imported. When I download the photos to my Desktop and try to import them, it is showing the message "preview unavailable for this file".
I can't really explain it butI read somewhere it has to do with Finder.