This is not a built-in feature of Firefox; you would need an add-on for this. Although the Tab Mix Plus extensions lets you force all links (and bookmarks) to open in a new tab, I'm not aware of any extension that forces them all to open in a new window. Hopefully someone else has a suggestion.

Jscher2000, Thanks for having a shot at it. There was no check box for 'this was helpful but not quite the answer, but I appreciate it' or I definitely would have checked that. Cordially, Dv

The only way I know to force links to open in a new window is setting the browser.tabs.opentabfor.middleclick pref to false and middle-click the link instead of Shift and left-click.
I also am not aware of an extension that force a new window with a simple left-click (all extensions focus on a new tab).

Cor-el, Thanks for the response. I'm not even sure what a middle click is and I'm worried about messing with pref files, so I guess I'll just leave well enough alone. Cordially, Dv

I cannot get anything to open in a new window either. In options>tabs, the box is checked that says "Open new windows in tab." When I try to uncheck it, it won't! I can click on it all day and the box will not uncheck.

If you want to try a Greasemonkey userscript, I posted one.

To use it, you first need to install the Greasemonkey extension: https://addons.mozilla.org/firefox/addon/greasemonkey/

Next, visit this page to install the script: http://userscripts.org/scripts/show/149337. I've only tested on Windows 7, but I don't think it should behave differently on Mac.

Originally, I had the script change every link regardless of the destination, but this made navigating around a site very annoying, so I changed the script to only change links to external sites. You can switch this by editing the script as described on the above page.

Please note that userscripts.org is not a site where you can trust everything you read. Bad actors routinely post scripts that steal cookies (allows session hijacking) and even add enthusiastic fake reviews. Shop with caution.

Hi mikmik, that sounds like a different problem.

Have you installed any tab-related add-ons that might alter the dialog? For reference, I have attached a copy of what I think is the default dialog.

You could try editing the setting using Firefox's about:config preference editor:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the filter box, type or paste link.open and pause while the list is filtered. These are the key preferences:

browser.link.open_newwindow

3 = divert new window to a new tab (default) (checked*)
2 = allow link to open a new window (unchecked*)
1 = force new window into same tab

* First checkbox in Options > Tabs (on Mac, Preferences > Tabs)

browser.link.open_newwindow.restriction

0 = open_newwindow preference honored for all new windows
2 = open_newwindow preference honored for all new windows except script windows with features (default)
1 = open_newwindow preference ignored completely (same effect as open_newwindow=2)

browser.link.open_newwindow.override.external

-1 = open_newwindow applies to external links (default)
3 = open external links in a new tab
2 = open external links in a new window
1 = open external links in active tab

Great idea. I did find a selection box in the tab options after I disabled Tab Mix Plus, but what I unchecked was the 'open bookmarks in a new tab,' and then I was able to uncheck that button.

This is a bother as well by having to hold the control key if I want a new tab, but that is easy enough anyways, and now the shift key works.

But I thought of about:config and wasn't sure what to look for, so your solution is perfect. Thanks again, and sorry for being off topic. And to those who suggested Grease Monkey, thank you also. I am just too lazy to use it, lol!