As far as links from external applications goes, the OS "default browser" as in the Windows Registry is used for opening the "browser"; and as far as within the built-in Profile Manager goes, the Profile labeled as Default = 1 in the profiles.ini file will be be used for the "default browser" in Windows.

A. I doubt if Mozilla will consider adding any new features to the built-in Profile Manager module or the user interface. In fact, two of the lead Mozilla developers have been "threatening" (for over 10 years, now) that "profiles" are going to be removed from Firefox altogether in the future; but no one has ever mentioned a time frame for that to happen.
https://bugzilla.mozilla.org/show_bug.cgi?id=214675 - first mention that I am aware of about removing the UI - and that was even before this browser used the Firefox name! (it was known as Phoenix originally, then called Firebird - but the trade mark holders of those names as they pertain to computers and computer software nixed licensing those names to Mozilla for a web browser)

B. A new Profile Manager application was finished back in 2011; which I suspect was prep-work for the removal of the "current" UI.
https://developer.mozilla.org/en-US/docs/Profile_Manager
http://ftp.mozilla.org/pub/mozilla.org/utilities/profilemanager/
There is a feature that allows the user to quickly change the "default" at will. Sorry, I haven't used that particular feature, so I can't comment on its efficacy for your purpose.

You should give that application a trial run.

As far as Chrome handles things, I have no idea. Chrome lasted all of 1 week on my PC's. The constantly running updater executable was Chrome's death sentence.

Do not confuse multiple windows in the same Firefox instance with using multiple profiles, as both are different.

If Firefox is already running then the link should open in the currently selected window if that window isn't a pop-up window (in that case it would be its parent window) or a new window can be opened.

You can set that via a pref on the about:config page.

You can override how external links are opened via the browser.link.open_newwindow.override.external pref.
The meaning of the values of browser.link.open_newwindow.override.external are the same as for browser.link.open_newwindow

• 1: current tab; 2:new window; 3:new tab;

• http://kb.mozillazine.org/browser.link.open_newwindow (3)
• http://kb.mozillazine.org/browser.link.open_newwindow.restriction (0)

If Firefox isn't running and needs to be launched with multiple windows opening then things might be different and I've never investigated what happens in such a case, so can't give advice how to deal with this.

@the-edmeister, thank you for your reply! I hope firefox doesn't ditch profiles -- I have to have a way to keep my different "personas" separate. Before I switched to chrome (when it added the "identity" feature), I was using a different browser for each business (plus one for the "personal" me). That was awful. I don't think the developers realize how useful this feature is -- the help for the profile manager says, "You normally don't need to create a new Firefox profile unless you are troubleshooting a specific problem with Firefox." Ha!

I tried the new profile manager, but it's pretty much the same as far as capability goes. I do appreciate your suggesting it though.

I guess chrome and firefox handle profiles/identities pretty differently. From what you said, firefox associates a particular profile (the default) with the default browser, whereas I guess chrome somehow doesn't make the association so restrictive so whichever chrome window was last active is used.

I have a soft spot for firefox and am kind of glad that chrome's cpu usage sent me back to it.  :)

What's the best way to make a feature request?

@cor-el, thank you for your reply! Sorry if I wasn't clear. Yes, I understand that a single instance of firefox can have multiple windows open, although I almost always use tabs. But I need to have separate cookies, bookmarks, etc for each business, so I need something like firefox's profiles or chrome's idenities. It's also extremely useful to be able to give each profile/identity a different skin/theme so that I have an easy visual cue to remind me which "persona" I am using. My "personal" profile has a violet skin, of course.  ;-)

See also:

• Multifox: http://br.mozdev.org/multifox/

@cor-el: Bummer, it doesn't seem to support different themes per multifox window. I appreciate your suggestion though!

I just switched back to Fx from Chrome after using Chrome for about 2 years.

I use two profiles with Chrome, one for work and another one is personal. They don't share anything which is exactly why I have two profiles and not just two windows. I found an extension for Fx to easily open two instances of Fx with different profiles but all links open in the same instance, which is not how it worked with Chrome.

With Chrome, whichever window was active last is getting the link which makes it perfect for multi-desktop use (on Mac OS X). I'm quite upset and annoyed that Firefox cannot do that. Isn't there *some* way?

You can add -no-remote to the command line to open another Firefox instance with its own profile and run multiple Firefox instances simultaneously.

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

• https://developer.mozilla.org/Mozilla/Multiple_Firefox_Profiles

Here is an idea, but I don't know if you can use it.

On your computer, create another user account. And more if you need. User A = job A, User B = job B . . . . . The Firefox profiles are kept in the Users folders. The setting of User A can be different from User B.

All you would need to do is; thru Windows, change to profile ZYX.

Right. That is entirely not what this is about.

I already run two separate Firefox instances with different profiles, simultaneously. That is NOT an issue.

Desired behavior: - have multiple Firefox instances running (instances A and B) - bring instance A to foreground - switch to a different application - click a link - link opens in instance A - bring instance B to foreground - switch to a different application - click a link - link opens in instance B

I don't know how to make this clearer. Always use the last active instance to open links?..

The point is that Chrome does exactly that and it's brilliant. Chrome also does some things that aren't brilliant which is why I want to switch back to Firefox but it's proving to be harder than I thought.

I went to the Mozilla Add-ons Web Page {web link} (There’s a lot of good stuff here), but could not find anything. If you do your own search you may find something.

Yeah, that's the thing... It really doesn't sound like an issue that'd be solvable by an extension. The event to handle (link click) is coming from the OS, not Firefox, so something needs to arbitrate and direct the event to the appropriate instance.

Thanks @diversario, you have explained the issue very well. I am reduced to cutting-and-pasting my links almost all the time now.  :( But at least Firefox rarely runs away with my cpu. :)

I'm glad to have 1 solutions next to my name but this issue is definitely not solved unless solution is to stop asking for it.

The "solution" to this thread is that there is no real solution for what the Owner of this thread wants to have happen.

That's a shame.

violetmoz, I hope you are seeing this. I found an old file I think can help you.

Usage: C:\PROGRA~1\MOZILL~1\firefox.exe [ options ... ] [URL]

      where options include:

 -h or -help        Print this message.
 -v or -version     Print Firefox version.
 -P <profile>       Start with <profile>.         <============================
 -migration         Start with migration wizard.
 -ProfileManager    Start with ProfileManager.
 -no-remote         Do not accept or send remote commands; implies -new-instance.
 -new-instance      Open new instance, not a new window in running instance.
 -UILocale <locale> Start with <locale> resources as UI Locale.
 -safe-mode         Disables extensions and themes for this session.
 -console           Start Firefox with a debugging console.
 -jsconsole         Open the Error console.
 -browser           Open a browser window.
 -new-window  <url> Open <url> in a new window.
 -new-tab     <url> Open <url> in a new tab.
 -preferences       Open Options dialog.
 -search     <term> Search <term> with your default search engine.
 -setDefaultBrowser Set this app as the default browser.

Check All the command line options

@FredMcD, I checked all the command line options, but don't see anything that will help. If there was one in particular you were thinking might help, please let me know.

@diversario, that was probably me that marked your reply as a solution ... the question I answered "yes" to was "was this helpful to you?" which is not the same as a solution, at all, at all. I just found your reply helpful in explaining the problem better than I had done. I suppose it is a moot point though, as there seems to be no solution within Firefox ... am now looking into other browsers.

Well. Good luck, Firefox.