Firefox – How to configure firefox to open links in the same window, but requests from external applications in a new window

I hate it, when sites decide for me, which links should open in a new window, and which in the same. The back-button doesn't work. Good thing is, firefox has the option browser.link.open_newwindow. If I set this to 1, all links with target=blank open in the same window, as it should be. But now also clicks in external programs (like the email-client or newsreader) on links open this in the same window, destroying the already opened website. How can I configure firefox to open links in a website always in the same window, but in external programs opened URLs always in a new one?