Nope, you don't miss something obvious... this feature just doesn't exist in Indesign.
you may have a look here for further information:
Not what I wanted to hear.
such is life.
I'm using CC 2017 It does this for me. When i click on the Link it opens a different Tab. and Every time you click the link it does what you want opens a different Tab every Click. Maybe its a limitation in CS6
Hm. I don't think, that something changed on that behavior in the last years.
Just tested that with InDesign CC 2017, exported to Interactive PDF and opened with Firefox' PDF reader.
OSX 10.10.5, Firefox 50.0.2.
No new tab will be opened, If I simply click a link.
However I can right-click and have the option to open a new tab in the browser.
I Dont have video record capability. But the Word HELP is The button when i click it i have it set to Amazon.com. Every time i click it it opens a new tab. I might be misreading the question. However i'm also viewing the PDF in Acrobat and not straight off the internet. However i would assume that it would have the same result.
I think i see the problem now. If you open it in the browser itself it does act different. It does not open a different window each time. Also My firefox wont work with the Interactive DOC but Chrome will. IF i'm not mistaken Interactive documents are kinda hit and miss when published on the web. Sometimes they work and other times they dont.
If a link or a button is clicked in a PDF opened with Adobe Reader Desktop:
The browser's preferences can change the behavior from "open in new window" to "open in new tab".
And there are browser plug-ins like "Tab Mix Plus" for Firefox where you can do additional controls for links that were triggered from external apps like Adobe Reader etc.pp.