The attached document is the crash report that was sent to Apple for the most recent attempt.

There was no attached document. Did you mean the information given in "more system details"? It shows:

Crash ID

The reports go to Apple. I tried to cut and paste the most recent report into the "Details" box, but it's apparently way too long.

More Information

My Apple software is up to date. I can't check plug-ins since I can't actually access Firefox. The same thing happens when I try to start it in "safe" mode.

Installed Plug-ins

In Safari, I have the usual plug-ins - Java, QuickTime, Shockwave, etc. I don't know for sure what all I have/had in Firefox, but they would be similar.

It may help if you could give us a Firefox Crash ID, from when the problem began. See Troubleshoot Firefox crashes (closing or quitting unexpectedly) for how to get a crash Report ID.

In any case, can you get a screenshot of what that unfamiliar Mozilla Firefox window looks like when you now try to start Firefox, or describe it better? The rainbow wheel of death seems like Firefox hangs or is not responding - How to fix at startup now.

Can you at least get to the "Firefox Safe Mode" window that lists different options, when you try to restart in Firefox Diagnose Firefox issues using Troubleshoot Mode? If so, try continuing into Safe Mode. See the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for what to try next.

I've tried fiddling around with this some more. If I check every single option on the "safe mode" window, Firefox will load. However, when I try to close it, it crashes. I just sent a crash report to Mozilla with the most recent crash (about 10 minutes ago). I really don't know what to do next.

The document I tried to attach was the actual report sent to Apple. However, it says that there is an error in uploading it -- maybe because the document (saved in Word) is 90 pages long? I also did a screen capture of the unfamiliar page and tried to attach it, with the same result -- error in uploading.

Thank you for your help!

An Apple crash report doesn't give useful information.

If you have submitted Breakpad crash reports then post the IDs of one or more Breakpad crash reports (bp-xxxxxxxx-xxxxxxxxx-xxxx-xxxxxxxxxxxx).
You can find the IDs of the submitted crash reports on the about:crashes page.
You can open the about:crashes page via the location bar, like you open a website.

See:

• http://kb.mozillazine.org/Breakpad (Mozilla Crash Reporter)
• https://support.mozilla.com/kb/Mozilla+Crash+Reporter
• https://developer.mozilla.org/en/How_to_get_a_stacktrace_for_a_bug_report

You said, If I check every single option on the "safe mode" window, Firefox will load. However, when I try to close it, it crashes.

Are you checking all of the options in the Firefox Safe Mode window shown here, http://kb.mozillazine.org/Safe_Mode#Safe_Mode_options and then clicking on "Make changes and restart"? If you do that, then when Firefox restarts, it will be in normal mode but with all add-ons (plugins and extensions) disabled and the default set of preferences, localstore, bookmarks and searchplugins. (I wouldn't do all that at once; you will lose all customizations.)

If, however, you check all the options and click "Continue in Safe Mode" then clicking those options accomplishes nothing, and you are running in Safe Mode which does NOT disable plugins. Crashes when you close Firefox could be related to a Java plugin bug that crashes Firefox when closing pages with Java applets. Mozilla just released Firefox 8.0.1 that resolves this, so you could try updating to Firefox 8.0.1 which is now available for download, from www.mozilla.com

Ref: http://www.mozilla.org/en-US/firefox/8.0.1/releasenotes/

Fixed Mac OS X crash that occurred in certain instances when a Java Applet is loaded with Java SE 6 version 1.6.0_29 installed.

P.S. Like cor-el said, do get the IDs of the submitted crash reports on the about:crashes page or better yet, post a link to the latest crash report. You can open the about:crashes page via the location bar (address bar), like you open a website.

This is the number of the latest crash report:

bp-de84911d-5ef6-4c38-b17f-efdc82111121

Here is the crash report:
https://crash-stats.mozilla.com/report/index/bp-de84911d-5ef6-4c38-b17f-efdc82111121

Firefox 8.0 Crash Report [@ mozilla::plugins::parent::_forceredraw ] 

Related bug: 700835 RESOLVED FIXED [Mac] Firefox 8 and up crash with Apple's latest Java updates for OS X 10.6 and 10.7 closing tab/window containing Java applet

Mozilla just released Firefox 8.0.1 that resolves this bug so you should update Firefox, either by using the built-in updater (see Update Firefox to the latest release) or by downloading and installing Firefox 8.0.1 from www.mozilla.com

I updated Firefox earlier today and have had no more problems so far. Thank you for all of your help!