I assume that you are referring to a JavaScript file. Java and JavaScript are different languages. To avoid confusion, see:

• http://kb.mozillazine.org/JavaScript_is_not_Java

If the server sends the file as text/plain then Firefox will open the file in a tab if you left click and not offer to download/save the file. In that case you need to save the file via the right-click context menu or the File menu.

You will have to right-click the link and use "Save Link As" to save such a file directly instead of left-clicking the link.

Thank you, your solution worked.

However, I did actually mean a .java file, this one actually: http://term.1.s3.amazonaws.com/Starter%20Files/T1_L29_Template.java

Is there an addon or settting that would allow it to have the open/save box by default, like in IE and Chrome?

That file is send as "Content-Type: application/x-unknown-content-type" and Firefox offers to save the file for me, so in this case it shouldn't be necessary to use this workaround.

That is strange. For me, Firefox opens it in a new tab like in the following screenshot, and does this on both my PCs:

It is possible that this has been changed server side and that the file was previously send as text/plain and that you still have that version in the disk cache.