Type about:config in the URL bar and hit Enter.
Acknowledge that you want to access that "page".

"Search" this pref at the top of that window.
dom.disable_window_open_feature.menubar

Double-click that pref to toggle it to True.

Thank you!

This information is better than one might think. In about:config, don't enter the whole "dom.disable_window_open_feature.menubar" in the search box, just enter "dom.disable_window_open_feature" and like ten variables pop up. I double click all of them that are false until every single one is true. ~~~~~ You see, I have a related problem. Somehow I have an odd keyboard problem and when typing fast it does some ctl character thing and opens a new tab. This is fine if your window has tabs, but when I compose an Email in sonic's webmail, it opens a new window that doesn't allow tabs. So when I'm writing a long involved Email and accidentally open a new tab, it just destroys my existing window and I'm looking at a window I can't get back from.))))))))((((((((((. But I just made all those false into true, went to my web mail, hit compose and Viola! it opened a window that allows tabs (and address & menu and everything!) Yippee! No more "screwed because I didn't take precautions" problem (the address is available in a tabless window, I copy it, open a new firefox window regularly and paste the address in and it works (with a whole lot of effort) and now, I can forget it all as it can no longer go wrong............Now that other problem ... I'm typing along at high speed and all of a sudden everything turns blue (yes, somehow inadvertently hit ctl-a, dunno how) and before I can stop myself, I've hit the next key and all the blue and all my typed text is gone as I look at that one lone character on the screen where all my beautiful thoughts just whoosh disappeared from. I'm thinking keystroke logger, when this happens, I just grab the buffer up until two keystrokes from the end and paste it all back. Can't be that simple.........maybe something to disable ctl & special characters while I want to type just pure text (have to hold down four keys to re-enable). Don't know if such a thing exists. maybe I'll ask formally, but I'm just overjoyed at solving a dumb problem really quickly......Thank you "the-edmeister" VERY MUCH!!!..oh, also need an automatic ctl-a ctl-c for just before I hit "post reply" or "submit" so when this disappears, it's not gone...pcG

See also;

• http://kb.mozillazine.org/Prevent_websites_from_disabling_new_window_features