Although I don't know what causes the problem you can try a few things:

First of all update Firefox. In your System Details attached to the question I can see that you are using an outdated version. https://support.mozilla.org/en-US/kb/update-firefox-latest-version

Second you can try going to about:config, accept that you will be careful, search dom.allow_scripts_to_close_windows and make sure it's set to false, otherwise other scripts might kill your session. If it's set to true, just double click it to change it. Restart Firefox, just to be save, and try if it helped.

In your Plug-Ins list I can also see one just called "5.1.40728.0". As I do not know what this is or what it does, it might be the cause of you problems. Consider uninstalling it if you know what you are doing.

If this does not help I would recommend you to read https://support.mozilla.org/en-US/kb/firefox-crashes-troubleshoot-prevent-and-get-help Especially the last point "Get help fixing this crash" could help me analyze the issue, but no promises :D Keep in mind that if your problem is not a crash but more a "regular" close the about:crashes tab might be empty. Also don't forget to make backups before you reset you Firefox or you might lose your personal data.

I jump between Firefox and other programs all the time Win 7.

In the address bar, type about:crashes<enter>. Note: If any reports do not have BP in front of the numbers/letters, click it and select Submit.

Using your mouse, mark the most resent 7 - 10 crash reports, and copy them. Now go to the reply box below and paste them in.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

I have received several replies, and I thank you all. The recommendations were helpful in that I am learning quite a lot. Seems like I still have a lengthy reading list. Unfortunately my problem has persisted. I did find some crash reports (attached), but I doubt they are going to solve the problem either as there were only three of them, and I find firefox closes like this many times every day.

FredMcD said

Using your mouse, mark the most resent 7 - 10 crash reports, and
copy them. Now go to the reply box below and paste them in.

---

Type about:support in the address bar and press Enter.
Under the main banner, press the button; Copy Text To Clipboard..
Then in the reply box at the bottom of this page,
do a right click in the box and select Paste.
This will show us your system details.
No Personal Information Is Collected.

bp-eb0b4d83-97eb-409d-8125-9cf502150926

Product Firefox Version 40.0.3

Release Channel release OS Windows NT OS Version 6.1.7601 Service Pack 1

The crash report flagged these programs;

Signature CLocalEndpointEnumerator

This is for Sumo's Related Bugs 731812 NEW --- crash in MMDevAPI.dll when inserting or removing a usb headset

Were you using a headset? Run Firefox without it.

Although I do use both a wired, and a bluetooth headset from time to time, this problem continues when neither are in use.

I've called the big guys to help you. Good luck.

I am computer challenged but have every confidence in those who have stepped up to offer support. We will solve this problem.

Znert said

In your Plug-Ins list I can also see one just called "5.1.40728.0". As I do not know what this is or what it does, it might be the cause of you problems. Consider uninstalling it if you know what you are doing.

I believe that this is silverlight.

The bug associated with the crash was reported with a list of troubleshooting steps that happened when they removed the bluetooth headset, but it sounds like it might be something else.

Forgive the typing out loud... Since its not an add on or ha, or the headset I might recommend trying to see if its the version of Firefox. The crash is from the previous version 40.0.3.

Also, might you have an example of a safe website where this can be reproduced, I might suggest to trouble extensions. These are not disabled in Safe Mode: Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

I had removed all extensions, and disabled hardware acceleration but my problem persisted until I removed the Plug-Ins. I rooted around in troubleshooting articles until I found out how to remove the references to the installed plugins, and removed them from the registry. I will start reconfiguring Firefox by replacing plug-ins one at a time, and hopefully will be able to share which was at the root of my trouble.

I thank all those who have contributed to my education. I may not yet be fully independant, but I am confident that I am more confident that I can do a better job of resolving issues in the future. My hats off to the support team that lurks in this program's background.

Good luck, and let us know what you find.