Firefox – How to make links with target=“_blank” open tab in current window

I don't use it personally, but it is said that NoScript can handle it:

Attempt to fix JavaScript links ( enabled by default): this means that NoScript will try to turn javascript: links into normal ones on untrusted sites as you click them, improving usability of the most unfriendly pages.

There used to be some standalone add-ons for this like Smart Middle Click but they were abandoned or/and deleted from addons.mozilla.org. I used to use Smart Middle Click, it is compatible with Firefox up to 3.6, haven't checked in newer versions. It is now removed from the web, but I recovered it from my disk.

To try if it works, unzip the contents to C:\Documents and Settings\<username>\Application Data\Mozilla\Firefox\Profiles\<profileID>.default\extensions and in about:config add preference extensions.CheckCompatibility.6.0 = false, or override version info in install.rdf file after unzipping.

However "fixing" JavaScript link is very hard in general (I mean creating a script that would work in all occasions), it's much easier to do it per-website (see how the website behaves and provide website-specific fixes as a GreaseMonkey script for instance).

It is a sign of bad JavaScript writing if some links can not be opened via middle click, if you have some particular websites that you visited often and can't make it work, you could try to contact their webmasters to indicate it.

This answer from Mozilla support seems to be useful. Quoting from there. You need to set the values marked italic. Just checked with FF v.23.0.1/Windows.

In a new tab, type or paste about:config and press Enter.
Click the button promising to be careful.
In the filter box, type or paste link.o and pause while the list is filtered.
Double click these and set the value as desired:

(A) 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

(B) browser.link.open_newwindow.restriction - for links in Firefox tabs

0 = apply the setting under (A) to ALL new windows (even script windows)
2 = apply the setting under (A) to normal windows, but NOT to script windows with features (default)
1 = override the setting under (A) and always use new windows

(C) browser.link.open_newwindow.override.external - for links in other programs

-1 = apply the setting under (A) to external links (default)
3 = open external links in a new tab in the last active window
2 = open external links in a new window
1 = open external links in the last active tab replacing the current page