Can't open Firefox, computer thinks it is already open

just got a new iMac, and wanted to transfer all my old Firefox info from my old machine. I downloaded the newest version of Firefox, and it seemed to work fine. Then I tried to move my profiles to the new machine (both on same network). Then I don't know what happened. I had to close Firefox for some reason, and when I tried to reopen it was told by my Mac that "A copy of Firefox is already open. Only one copy of Firefox can be open at a time". I checked in Finder to see if I could force-quit Firefox, but according to Finder firefox was NOT running.
I first did a restart of the computer, but when I tried to open Firefox got the same message. Then I threw my Firefox application away and downloaded a new one. No help, same error message.
So how do I convince my Mac that Firefox isn't already running? Help, please!!!

Repairing permssion instructions are listed in the os Help menu and within Apple's Knowledge Base articles - http://docs.info.apple.com/article.html?artnum=25751

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Unable to open firefox, dialogue box says program already open but not as far as I can see.

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I am using IE to post this message on Firefox.
It has happened again. At 23:05 (UK time) I openedFirefox on the firefox site not IE. I opened my btinternet.com email account but at 23:41 the tab had not opened fully and still trying to load. I closed firefox and tried to open it again and here are the correct details of the dialogue box which appeared.
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I suspect you need more expert help but here are a few things you can try.
If you can't open Firefox(double click on Firefox desktop icon) try Safe Mode - Hold down the Shift Key as you double click on the icon>don't check anything on the page that opens>continue. If Firefox opens and works in this safe mode go to Add-ons> Extensions and look for "Ask". Then look at Add-ons >Plug-ins and again look for "Ask" . Remove, delete,disable any Asks. If you do remove any, close Firefox. And try again in Normal Mode.
The Ask website has detailed instructions for removal but you need to find it on your computer and have your computer in working order.
If there is no sign of Ask and Firefox is working well in Safe Mode you should work your way through this -
https://support.mozilla.com/en-US/kb/Troubleshooting%20extensions%20and%20themes
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Every time I open Firefox I get another window that opens over the homepage. It is almost blank with a few lines at the top of the page and the words user registration. It has been happening ever since Firefox updated on my computer yesterday, even after uninstalling and reinstalling.

'''Try Firefox Safe Mode''' to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.
''(If you're not using it, switch to the Default theme.)''
* You can open Firefox 4.0+ in Safe Mode by holding the '''Shift''' key when you open the Firefox desktop or Start menu shortcut.
* Or open the Help menu and click on the '''Restart with Add-ons Disabled...''' menu item while Firefox is running.
''Once you get the pop-up, just select "'Start in Safe Mode"''
'''''If the issue is not present in Firefox Safe Mode''''', your problem is probably caused by an extension, and you need to figure out which one. Please follow the [[Troubleshooting extensions and themes]] article for that.
''To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.''
''When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.''

When i open firefox, a small "user toolbar" window opens on top right hand side, i dont want that.

When i open firefox, a small user toolbar window opens in top right corner, please help as i dont want it, i close it but it takes to much of time to close and it hings up a bit evrytime.

This could be a feature of an add-on. Could you check to see whether you have any unrecognized add-ons and disable (or remove) them. In particular:
orange Firefox button ''or'' classic Tools menu > Add-ons > Extensions category
Then restart Firefox and watch for the toolbar, which hopefully will not appear.
You also could paste a list of your extensions here for review. You can copy them from this page:
Help > Troubleshooting Information
It's the second table, which appears below the Extensions heading.

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Came home to find computer restarted, which I assume is an automatic Firefox update.
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*https://support.mozilla.com/kb/Firefox+hangs

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Are you doing that ?
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* see [[Firefox hangs or is not responding - How to fix#w_firefox-hangs-when-you-quit-it]]_firefox-hangs-when-you-quit-it
* this explains how to check & if necessary kill the process [["Firefox is already running but is not responding" error message - How to fix it#w_end-firefox-processes]]_end-firefox-processes
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[[How to fix preferences that won't save]]
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* https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes
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*In Firefox 29.0 and above, click the menu button [[Image:New Fx Menu]], click Help [[Image:Help-29]] and select ''Restart with Add-ons Disabled''.
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When the Firefox Safe Mode window appears, select "Start in Safe Mode".
:[[Image:Safe Mode Fx 15 - Win]]
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''To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.''
When you figure out what's causing your issues, please let us know. It might help others with the same problem.

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Could you check whether you have dual homepages?
orange Firefox button ''or'' classic Tools menu > Options > General
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More info: [https://support.mozilla.org/en-US/kb/How%20to%20set%20the%20home%20page How to set the home page | How to | Firefox Help].
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I will only close the browser by using your suggestion, File > Exit, from today on, and see what happens. Thank you for your expedient reply.

Can't open Firefox, computer thinks it is already open

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