Try this extension - https://addons.mozilla.org/en-US/firefox/addon/profileswitcher/

You can open two profiles at the same time by starting a second instance via the -no-remote command line switch. You can't open an external link in an instance that is started via -no-remote unless you would drag the link to that instance, but if you always want to open an external link with a specific profile then that shouldn't pose a problem as long as you start that instance without using the -no-remote switch.

See:

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

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile

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

Thanks for the ideas! As I mentioned, I have been using multiple accounts already. It took effort to set up, but I have shortcuts for all profiles in my Windows start menu. That part works fine, so the profile switcher does nothing for me that my Windows shortcuts don't already do for me.

The problem is that every time I click a link in an other application, like Thunderbird, a window with the default profile is opened. So when I have a window open from my 'Private' account, my 'Work' account is opened anyway. On top of that, I get this dialog: Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window.

This is why the multiple account solution works for me. To separate my work and private stuff I only need to change the contents of my bookmarks bar, so I hoped there was some trick to maintain to groups of bookmarks.

You can't get Firefox to work as you are explaining you want. The Default Profile can't be changed on-the-fly to the Profile you are currently using. That message "Firefox is already running ..." comes up due to you or "something" trying to open a 2nd (or subsequent) Profile, unless that -no-remote command was used to open the additional Profile. And -no-remote won't work to open the Default Profile without causing issues with how Windows works with "calling up" the Default Browser.

In response to your last statement - "To separate my work and private stuff I only need to change the contents of my bookmarks bar, so I hoped there was some trick to maintain to groups of bookmarks."

This extension will allow you to change the Bookmarks Toolbar folder while you are using Firefox. https://addons.mozilla.org/en-US/firefox/addon/set-as-bookmarks-toolbar-folde/ I just installed that extension and verified that it still works in Firefox 35. There is a context menu item added for "Set as Bookmarks Toolbar Folder"' that appears when the Bookmarks Menu Bar drop-down menu is used (not in the Library window or the Bookmarks Sidebar). That menu item appears when you right-click a folder in the Bookmarks Menu folder. It doesn't appear with the "Bookmarks Toolbar" folder or the "Unsorted Bookmarks" folder - only a folder that is in the "Bookmarks Menu". That should "solve" wanting to have two different settings for the Bookmarks Toolbar, but the Default Profile "thing" is still an issue for what you are trying to accomplish. I don't "see a fix" for that - without resorting to a 2nd Window User Account which is what I thought you were referring to by "I've been using two user accounts to achieve this" in your initial posting. And since the Menu Bar is hidden by default these days, you can use Alt then B to open the Bookmarks drop-down from the "revealed" Menu Bar so you can access that "Set as Bookmarks Toolbar Folder" menu item - without having to show the Menu Bar all the time.

BTW, using "accounts" in lieu of "Profiles" can be confusing when discussing Firefox Profiles.

Thanks, that is exactly what I meant. Sorry for the profiles/accounts mixup. It takes a few actions too many to change the bookmarks, but I'm gonna try it for a while!

You're welcome.