bump.

Open Windows Internet Explorer. Have it declared the default browser. Then close it. Open Firefox, and do the same here. Then close. After, test with a HTML file.

Didn't solve it. Still had to restart Firefox to make it work again, just like everytime I boot the PC.

If it helps, I tracked it down that this happens only when I run Firefox via Task Scheduler scheduled to launch on user Log in on Windows startup. So it has something to do with that.

Open the Task Scheduler. Carefully copy that command. Open the Actions menu. Copy the Program/Script and the Options. And post it here.

Program/Script: "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" Add Arguments: "https://www.facebook.com/" "https://twitter.com/" "https://www.google.com/ncr" (to open tabs on launch)

Exported .xml:

<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.4" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
  <RegistrationInfo>
    <Date>2015-09-21T20:49:18.54831</Date>
    <Author></Author>
  </RegistrationInfo>
  <Triggers>
    <LogonTrigger>
      <Enabled>true</Enabled>
      <UserId></UserId>
    </LogonTrigger>
  </Triggers>
  <Principals>
    <Principal id="Author">
      <UserId></UserId>
      <LogonType>InteractiveToken</LogonType>
      <RunLevel>HighestAvailable</RunLevel>
    </Principal>
  </Principals>
  <Settings>
    <MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
    <DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
    <StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
    <AllowHardTerminate>false</AllowHardTerminate>
    <StartWhenAvailable>true</StartWhenAvailable>
    <RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
    <IdleSettings>
      <StopOnIdleEnd>true</StopOnIdleEnd>
      <RestartOnIdle>false</RestartOnIdle>
    </IdleSettings>
    <AllowStartOnDemand>true</AllowStartOnDemand>
    <Enabled>false</Enabled>
    <Hidden>false</Hidden>
    <RunOnlyIfIdle>false</RunOnlyIfIdle>
    <DisallowStartOnRemoteAppSession>false</DisallowStartOnRemoteAppSession>
    <UseUnifiedSchedulingEngine>false</UseUnifiedSchedulingEngine>
    <WakeToRun>false</WakeToRun>
    <ExecutionTimeLimit>PT0S</ExecutionTimeLimit>
    <Priority>7</Priority>
    <RestartOnFailure>
      <Interval>PT1M</Interval>
      <Count>3</Count>
    </RestartOnFailure>
  </Settings>
  <Actions Context="Author">
    <Exec>
      <Command>"C:\Program Files (x86)\Mozilla Firefox\firefox.exe"</Command>
      <Arguments>"https://www.facebook.com/" "https://twitter.com/" "https://www.google.com/ncr"</Arguments>
    </Exec>
  </Actions>
</Task>

rhazor said

Program/Script: "C:\Program Files (x86)\Mozilla Firefox\firefox.exe"
Add Arguments: "https://www.facebook.com/" "https://twitter.com/" "https://www.google.com/ncr"

And all three open, Yes?

Of course.

As you saw, I do the same as you, and have had no problem. I've called the big guys to help you. Good luck.

Check the target field in the Firefox desktop shortcut and make sure that you do not start Firefox with the -no-remote switch or have set the environment variable MOZ_NO_REMOTE=1 (Control Panel > System > Advanced > Environment variables).

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

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