Hello.

Hopefully this support article is what you need:

https://support.mozilla.com/en-US/kb/Firefox+will+not+start

In any case, it's possible that you are having a problem with some Firefox add-on that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check), to see if Firefox goes back to normal?

Whenever you have a problem with Firefox, whatever it is, you should make sure it's not caused by one (or more than one) of your installed add-ons, be it an extension, a theme or a plugin. To do that easily and cleanly, run Firefox in safe mode (don't forget to select Disable all add-ons when you start safe mode). If the problem disappears, you know it's from an add-on. Disable them all in normal mode, and enable them one at a time until you find the source of the problem. See this article for information about troubleshooting extensions and themes and this one for plugins.

If you need support for one of your add-ons, you'll have to contact its author.

If the problem is not disappears when all add-ons are disabled, please tell me, so we can work from there.

You will get this error if the C:\Program Files\Mozilla Firefox\ has following files missing. application.ini & platform.ini. This files might be removed by some antivirus or other softwares. Try this out. It worked for me..

Get the files and try copying to the C:\Program Files\Mozilla Firefox\ folder.

Let me know if you dont have these files i can send it to you. depending on the version you have.

I had the problem of couldn't read application.ini for a long time. .. :-/

But finally, I found a solution!

Here’s a step-by-step instruction to get rid of the “application.ini” problem on Firefox:

Step 1. Uninstall Firefox by going into Control Panel > Add & Remove Program.

Step 2. Reboot your computer.

Step 3. Go to My Computer (C drive) > Programs > Mozilla Firefox

Yes. This is a strange part I found for “application.ini” file. It’s un-deletable, unmovable, un-uninstallable. :-/ I checked for viruses by scanning with 2 different software. No virus was found. Phew!

So here’s what I came up as a solution:

Step 4. Open the Program > Mozilla Firefox folder.

Do you have the source of error, application.ini in the folder? Try to remove it or move it into the Recycle Bin, because it's impossible...

Step 5. Click on Back icon until you are back to Step 4, to see the Mozilla Firefox folder. Rename the folder with anything you like, such as “useless junk” etc. except “Firefox” or “Mozilla”.

I named the file as “unused”.

Step 6. Go to Firefox website and install the new Firefox.

Done!

If this doesn’t work, let me know! :-)