I promise I had line breaks in that post for readability. Oh well!

I just now successfully installed and opened Firefox Developer Edition, if that is useful info.

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

Thanks for your detailed response. No luck. I tried the steps as recommended: (1) Opened Windows Firewall, removed Firefox (there were 2 of them), added it back. I ticked all 3 boxes in the entry. (2) Ran EnumProcess, with these results: Windows Firewall is on 2 processes from Symantec Corporation detected (3) Checked all Symantec logs I could find, but no entries were found corresponding to my FF crash. (4) Updated Symantec, then temporarily disabled Symantec. No change. (5) Also dug thru Symantec options for anything resembling a list of allowed programs, but didn't find anything.

What would you recommend I try next?

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select Network. Look for Configure How Firefox Connects and press the Settings button. If you are using a proxy, make sure those settings are correct. If there is no proxy, first use No Proxy. If there is a problem, then try System Proxy.

You said you had crash reports.

If you can't get Firefox to open, you will have to do this the hard way. https://support.mozilla.org/en-US/kb/mozillacrashreporter Open the file browser / explorer on your computer. Note: You may have to enable Show Hidden Folders / Files. Enter this in the address bar;

Windows: %APPDATA%\Mozilla\Firefox\Crash Reports\submitted Win 7/Vista: C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Crash Reports\submitted Win XP/2000: C:\Documents and Settings\<username>\Application Data\Mozilla\Firefox\Crash Reports\submitted

Mac OS: /Users/<username>/Library/Application Support/Firefox/Crash Reports/submitted Linux: /home/<username>/.mozilla/firefox/Crash Reports/submitted

Copy the last 5-7 Recent File Names in the folder. Post the information in the reply box below.

Re: proxy - I never get an address bar so unfortunately I won't be able to try that step. Here are the file names: bp-264db6e3-a33d-439d-8288-454262170206.txt bp-532be8a7-57a5-4f24-86ab-f90b02170206.txt bp-538704d0-ada2-447b-b89b-62fef2170206.txt bp-604f8af3-240e-487e-99ab-e85312170206.txt bp-be1bba16-209a-4285-8b8e-63baa2170207.txt bp-f12a4863-a7ea-4a34-82e6-381262170206.txt bp-f8c55a76-5094-4278-97c9-04c242170206.txt

Product Firefox Release Channel release Version 51.0.1 Build ID 20170125094131 OS Windows 7 OS Version 6.1.7601 Service Pack 1

All the reports are the same;

Signature: qipcap.dll@0x31100

This is for Sumo's Related Bugs 682912 REOPENED --- qipcap.dll WebSense Content filtering dll crashes Firefox on launch

Unfortunately, this crash is caused by the Websense/Forcepoint security software that is running on your device.

If that's in a corporate environment - please get in contact with your IT department to make sure that Websense is fully up to date, as it has the tendency to crash newly released Firefox versions until they adapt accordingly.

Another option would be to install an esr version of Firefox:

Thank you! That's exactly what I needed to know. I'll chase down those options from my end. Have a great week!

See also:

• https://support.mozilla.org/kb/websense-startup-crashes-firefox