Since I'm not quite sure what steps you followed, I'm going to suggest the following:

(1) A "Clean Reinstall" of the Firefox program files (does not touch your settings) (2) Creating a parallel settings folder, also known as a new profile (also does not touch your settings)

This will get us as close to a factory fresh install as possible to see whether that runs. If that does not run, there may be a severe incompatibility with driver software or something else on your system. If it does run, we can review options for moving bookmarks and other personal data to the working profile.

Here are the steps:

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. Do NOT uninstall Firefox, that's not needed.

(1) Download a fresh installer for Firefox 38.0.5 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

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

(3) Rename the program folder, either:

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(4) Run the installer you downloaded in #1. It should automatically connect to your existing settings.

Can you get Firefox reinstalled?

Note: Some plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

Create a new Firefox profile

A new profile will have your system-installed plugins (e.g., Flash) and extensions (e.g., security suite toolbars), but no themes, other extensions, or other customizations. It also should have completely fresh settings databases and a fresh cache folder.

Exit Firefox (if applicable) and start up in the Profile Manager using Start > Run, type or paste the following and press Enter:

firefox.exe -P

A small Profile Manager dialog should appear. Don't delete anything here!

Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like TEST062115, and skip the option to relocate the profile folder. After creating the profile, select it and start Firefox in that profile.

Will Firefox start up?

When returning to the Profile Manager, you might be tempted to use the Delete Profile button. But... it's a bit too easy to accidentally delete your "real" profile, so I recommend resisting the temptation. If you do want to clean up later, I suggest making a backup of all your profiles first in case something were to go wrong.

If you are still having problems,

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: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.

Some problems occurs 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}

jscher2000, I did the step for clean install, but once I run the new installer for Firefox 38.0.5 and once it is complete it to begin running Firefox, it crashes once again and does not allow me to do anything, the mouse can move around the screen but that is all it does i have to do a hard restart on the pc (holding the power button until it shuts off). I i already have a file for the old Firefox files on my desktop the last time it crashed and i was able to save the files and profiles. at this moment I'm unable to save the new profile settings nor access the Firefox program without crashing it or my pc again (for the 6th times).

My Firefox began crashing on startup. Attempts to do a simple reinstall made no difference. Atttempts to use firefox.exe -p also crash. (This message: Problem signature:

 Problem Event Name:	APPCRASH
 Application Name:	firefox.exe
 Application Version:	40.0.3.5716
 Application Timestamp:	55dda065
 Fault Module Name:	StackHash_0a9e
 Fault Module Version:	0.0.0.0
 Fault Module Timestamp:	00000000
 Exception Code:	80000003
 Exception Offset:	00130778
 OS Version:	6.1.7601.2.1.0.768.3
 Locale ID:	2057
 Additional Information 1:	0a9e
 Additional Information 2:	0a9e372d3b4ad19135b953a78882e789
 Additional Information 3:	0a9e
 Additional Information 4:	0a9e372d3b4ad19135b953a78882e789

Eventrually I manually moved my old profile. Then reinstalled again. Firefox worked but of course I lost all my bookmarks history etc. Then I tried to copy back the old profile, It worked and I got back my bookmarks and history (very important). But after I closed down and restarted my computer things were back where we started. Firefox crashing on startup.

Did you copy the whole profile? Sounds like one of the files is corrupt. Did you copy, or move the old to the new? If you copied from the old, then we can try again.

Warning ! ! Only Copy the files you are told. We will avoid anything that might be the cause of your problems. Here is the list of files;

cookies: Do not bother. Cookies will be created when you return to the web site. However, you will have to log in everywhere.

extensions(add-ons): it would be better to download them fresh.

==============

key3.db and logins.json: These are the Password files.

mimeTypes.rdf: What to do with what type of file.

places.sqlite: History and Bookmarks.

prefs.js: Your settings. Note, this may be contaminated.

Copy these files from the old to the new. You will get a message about the files already exist. Choose to over-write for each file.

Thanks FredMcD, that's very useful as I wasn't sure which files to keep and may well have copied one that was corrupted. I'll look at those files in more detail later. NB: Interesting: Someone else suggested I edit the prefs.js file adding the line: user_pref("layers.d3d11.disable-warp", true); This may have worked but it concerns me that I don't know if it could be harmful. Do youknow? I will follow your instructions later when I have time.

iantwebb said

Someone else suggested I edit the prefs.js file adding the line: user_pref("layers.d3d11.disable-warp", true);

I don't know what that does. Mine is false.

iantwebb said

Someone else suggested I edit the prefs.js file adding the line:
user_pref("layers.d3d11.disable-warp", true);
This may have worked but it concerns me that I don't know if it could be harmful. Do youknow?

"Warp GL" support was added in Firefox 37 and relates to accelerating certain kinds of graphical operations. You can enable/disable it using about:config instead of directly editing prefs.js:

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

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

(3) Double-click the layers.d3d11.disable-warp preference to switch it from false to true

I don't know whether this takes effect immediately or after you exit and start Firefox up again.

Firefox worked fine after the above even after being closed and restarted, BUT once again after I shut down the laptop and restarted it the same problem recurred (ie Firefox not starting). So I will now try to follow your plan regarding creating a new profile and copying only the essential files. Clearly whatever the problem is it somehow becomes activated by Windows shutdown and restart.

If you have any utility software that runs at Windows startup and includes a feature to clean your browser data, that might be one explanation for settings changes. For example, some users with CCleaner have had issues settings or add-ons being removed (I can't recall the details).

Thanks for sticking with this. I don't see any evidence that ccleaner is running nor do I have any program set to clear browser history. Both Chrome and Internet explorer are working fine and normally. I have been using Firefox since the earliest versions and Netscape before that. This is increasingly distressing as I just cannot get Firefox to run after each time my computer is restarted. OK so one has uninstalled and reinstalled over and over. I have put the old profiles in renamed folders and files to keep them out of the reinstall. Any thoughts what to do next?

I didn't mean to sidetrack you from trying a new profile. Or did that have the same problem?

I am not sure. Before the last reinstall i moved the old profile to the desktop and the reinstall seems to have created a completely new profile. But this has not enabled Firefox to open

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

Sorry no. I have tried that after after every startup failure. You get exactly the same message as when you start it normally. By the way my OS is Windows 7 64 bit)

You said your profile was safe on the desk top, yes? What I want you to do is totally remove Firefox, and the profile folders. BUT NOT the profile on the desk top.

Download Firefox Full Version For All languages And Systems {web link} Save the file. Then;

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. Linux: Check your user manual.

• Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory.

Look for, and rename any Mozilla or Firefox folders by adding .old to them.

Now using the file explorer again, open this folder; C:\Users\=<user>=\AppData\Roaming\Mozilla and rename the Firefox folder by adding .old to it.

After rebooting the computer, run a registry scanner. Then run the installer. If all goes well, remove the OLD folders when you are done.

For now, use the new profile AS IS. Make no changes. Does it work?

If is works properly, then copy the files I described above. 10/5/15 9:17 AM

OK the first difference here is that all my previous installations were by "stub" setup files. I recently ran PCTools Registry Mechanic, but will now do so again after renaming the Mozilla folder in roaming. (There was no Mozilla folder in programs as I had deleted that earlier). THis will take a few minutes. Then I'll reinstall Firefox (41). If it works I'll then need to shut down and restart Windows to see what happens but as its already 2 am here I may complete that tomorrow!

No I am sorry to say I cannot get Firefox to work at all now. Here is the message: Problem signature:

 Problem Event Name:	APPCRASH
 Application Name:	firefox.exe
 Application Version:	41.0.1.5750
 Application Timestamp:	560b22a1
 Fault Module Name:	StackHash_0a9e
 Fault Module Version:	0.0.0.0
 Fault Module Timestamp:	00000000
 Exception Code:	80000003
 Exception Offset:	001b0778
 OS Version:	6.1.7601.2.1.0.768.3
 Locale ID:	2057
 Additional Information 1:	0a9e
 Additional Information 2:	0a9e372d3b4ad19135b953a78882e789
 Additional Information 3:	0a9e
 Additional Information 4:	0a9e372d3b4ad19135b953a78882e789

Read our privacy statement online:

 http://go.microsoft.com/fwlink/?linkid=104288&clcid=0x0409

If the online privacy statement is not available, please read our privacy statement offline:

 C:\windows\system32\en-US\erofflps.txt

Hi iantwebb, did we ever ask you to look for crash report IDs? If you are getting the Mozilla Crash Reporter form, your Firefox may have logged some data that would help track down the cause of the problem. You can submit that data to Mozilla and share it with forum volunteers to see whether it points to the solution. Please check the support article "Firefox crashes - asking for support" for steps to get those crash report IDs from the about:crashes page, and then post some of the recent ones here.

But if you only get a Windows dialog, then unfortunately that data won't be available.

Also, I don't think it was mentioned in this thread that there is a problem "going around" that causes nearly instant startup crashes:

Firefox is crashing within seconds of startup if you have either of the Applian Technologies programs Freecorder or Replay Media Catcher in combination with Norton security software (and possibly some other security software).

If you have either of those Applian programs and it isn't essential, try uninstalling it and then restarting Windows to ensure that none of its components are left running.

Will Firefox start normally after that?

(If you prefer not to uninstall the program, another user said he used msconfig to prevent FlvSrvc.exe from running at startup and that fixed it. See: https://support.mozilla.org/questions/1086722#answer-789197)

Should I delete those .old folders before trying to install? I do not have those programs and the crash reports folder is empty as far as I can see. I t ried %APPDATA%\Mozilla\Firefox\Crash Reports\submitted\ but it said windows cannot find that file