I'm not too sure why the difference between JavaScript and html (TARGET="_blank") popups in Firefox (or Opera and Chrome for that matter, which appear to behave the same). JavaScript opens a new window; TARGET attrib alone opens a new tab. This appears to be the default behaviour. IE8 and Safari open a new window in both cases (at least by default).
However, the browsers (apart from Chrome and Safari as far as I can see) do have a user preference as regards to Windows OR tabs.
In Firefox (3.5), tools > Options > tabs > "Open new windows in a new tab instead". Appears to be checked by default - but this does not influence JS popups.
Opera (10.10) has an opposite preference, tools > Preferences > Advanced > tabs > [Additional tab options...] > "Open windows instead of tabs". Which is NOT checked, but again does not appear to influence JS popups.
IE8's preference, however, does influence both JS and html popups. tools > internet Options > General > tabs [Settings] > "Always open pop-ups in a new window" (selected by default) OR "Always open pop-ups in a new tab". HOWEVER, IE8 does have the additional option, "Let internet explorer decide how pop-ups should open" - in which case it behaves the same as FF, Opera and Chrome - JS new window, html new tab!
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