Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

While still in Safe Mode,

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.

The crash report is several pages of data. We need the report numbers to see the whole report.

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.

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.

I've tried starting my iMac in Safe Mode, then opened a newly downloaded Firefox (downloaded via Safari), but I get the message that it crashes when opening. In my library list of Crash Reports/Submitted, I don't have any report newer than January 19, 2015.

  Thanks for your suggestions but I seem to be dead-ended with both of my attempts to follow the directions you provided.  Firefox works just fine on my MacBook Air laptop, but has failed badly just today on my iMac desktop.  Can't figure out why.

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

First try to start Firefox with the profile manager to see if its an extension: Profile Manager - Create, remove or switch Firefox profiles

Second, make a back up of the profile: Back up and restore information in Firefox profiles

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

To do a clean reinstall of Firefox, please follow these steps: Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • 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.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Please report back to say if this helped you!

Thank you.