I did find a way to make Shift-click open a new tab in Firefox: open browser.jar (under the firefox install dir, opens as a regular zipfile), and change browser.js. The relevant function is handleLinkClick(event, href, linkNode).
The only way to change the keyboard shortcuts that I’ve found so far is the extension keyconfig, which besides being user-hateful won’t let me assign both ctrl+n and ctrl+t to do the same thing. The best I can do it to disable ctrl+n, but that’s not exactly what I want to do.
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Good job, that’s ‘new window’ behavior is killing me.
He-he, now I going to find somewhere in the same .jar how to exchange Open link in new Window and Open link in new Tab in context menu :)