Strange! It sounds as though either:

• Firefox is not fully unloading the first time -- which will block Firefox from starting again, although usually it tells you that is the reason.
• Some other program started AFTER Firefox is blocking it from fully loading. This might be some kind of security or sandbox software that modifies how browsers interact with the system.

The next time this occurs, could you try "killing" Firefox using the Windows 7 Task Manager? You can call that up using Ctrl+Shift+Esc. Then click the Processes tab and look for firefox.exe and if you find it lingering there, right-click > End Process on it to crash it out.

Will it start after that?

One other thought. One of the main technical changes in Firefox 54 was to enable more individual content processes. In Firefox 48-53, the Firefox multiprocess feature would create one process for the UI and one process for content. Now Firefox will aim for four content processes. It's hard to see how this could cause the symptoms you're describing, but...

Could you test rolling back the number of content processes to 1? If this doesn't work, you could try reverting to single-process mode. Here's how you can try this:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste ipc and pause while the list is filtered

(3) If the dom.ipc.processCount preference is bolded and "user set" to 4, double-click it and edit the value to 1, then click OK

Presumably that will not take effect until the next startup, at which time you should check it to make sure it hasn't reverted back. Any difference?

Alternately, you can disable multiprocess mode using a different preference:

(4) In the search box above the list, type or paste autos and pause while the list is filtered

(5) Double-click the browser.tabs.remote.autostart.2 preference to switch the value from true to false

Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart

At your next Firefox startup, it should run in the traditional way. Any difference?

Killed Firefox exes after closing. There were 2. Tried to re open. It would not. Only 1 exe file found after that try. What next?

Tried refreshing Firefox. That didn't solve.

ipc count was set on 1

This is puzzling. If the program files are corrupted you can replace them, but why would Firefox even start once in that case?? Anyway, if you run out of ideas:

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. It's not essential to uninstall Firefox, but you can if you like, saying No to any request about removing personal data.

It only takes a few minutes.

(A) Download a fresh installer for Firefox to a convenient location. You can choose between:

Regular version for Windows 7-10 (54.0.1) https://www.mozilla.org/firefox/all/ Note: only runs Flash, no other legacy plugins "Windows" version is standard 32-bit version, which is generally recommended; to take advantage of more memory, you could switch to the 64-bit version, see: How to switch from 32-bit to 64-bit Firefox

Extended Support Release for Windows XP-10 (52.2.1esr) https://www.mozilla.org/firefox/organizations/all/ Note: Windows (32-bit) runs legacy plugins that ran in Firefox 51; 64-bit runs Flash and Silverlight. (If anyone reading this is thinking of switching to the 64-bit version, see: How to switch from 32-bit to 64-bit Firefox)

(B) Exit out of Firefox (if applicable).

(C) Using Windows Explorer/My Computer, rename the program folder as follows:

64-bit Windows users with 32-bit Firefox: Rename

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

Other Windows configurations: Rename

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.

Note: Some less used files may exist only in that OldFirefox folder, so I suggest retaining them for a few days in case we need to go looking for something in there.

Any improvement?

Thanks.

Haven't tried the clean reinstall yet. Did do the refresh, but that didn't help.

I did disable a Cisco Open H264 video codec plug in. Since this disable, I have been able to close/open firefox several times. I don't know what this plug-in is.

Only have 2 other plug ins. Shockwave and Widevine (by Google). Do I need these?

Here's my understanding:

• Cisco Open H264 video codec plug in - used for real-time communications such as video conferencing, mostly not necessary, interesting that disabling it helps
• Shockwave Flash (not to be confused with Shockwave for Director) - Flash player, used on many sites, but you can set its permission to "Ask to Activate" to control which ones use it
• Widevine (by Google) - allows you to play DRM-protected content on sites like Amazon Video, Hulu, and Netflix (see: Watch DRM content on Firefox)

Thanks for your help