The "old Firefox data" folder might have been created by Firefox if you used the Reset feature. You probably should retain it until you are 110% sure you don't need it. (More information: Refresh Firefox - reset add-ons and settings; Recover important data from an old profile.)

In case the problem is related to the home page, could you try starting up Firefox to a blank document? In the Start menu search box or run box:

firefox.exe "about:blank"

If that works, you might go to about:crashes and submit some of the IDs (again?) since I couldn't find the two I tried on the crash report server (https://crash-stats.mozilla.com/).

Did you try a clean new profile?

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

If the issue was with the plugins , it should not happen in Safe mode , the issue persists even in Safe mode .

New profile -I uninstalled the  browser and deleted all associated data and re installed it. 

Homepage-there is no homepage just "about blank"

The crash Id's

d9873438-ab43-4b79-924e-7301b1916fdd

182e8d14-b17f-4d56-a208-a4716096accf

4c1e5192-777c-42c3-a62b-b03b1fed2c2d

80e88962-96c0-4055-bf7d-8c10c122884e

ed3db9f4-2c9e-4439-ab88-c45dde7dbf09

148545ce-8ec9-4194-90ba-6c17bdc85ce4

903d8dd8-5325-4431-a42c-b313d96d5d04

bp-24c71ca7-fe16-40ac-820c-9bb042120810

You are currently using a Firefox 15 beta release according to your system details list.

Do the crashes also happen with the Firefox 14.0.1 release and a new profile?

Previous versions of Firefox used to cause web pages to hang, freezing everything. Firefox 15.0.1 has gone one step further / It hangs immediately, as soon as the welcome message ( and the picture showing a kind of crop circle) appears. This means having to Force quit... I have done just that ( and relaunched ) three times, without success. I've also trashed FF and reinstalled it three times. No joy.

There may be a "fix" of some sort, but it shouldn't be necessary : Safari, Chrome, Opera, Camino, and SeaMonkey work fine "straight out of the box". So why not Firefox? 

Besides, a "fix" would be impossible since I'd have to launch FF to apply it, and as I said, it hangs/freezes immediately. I'm using a Mac, system 10.6.8.

Hi xkreiss, can you start up to the Safe Mode dialog and run in Safe Mode as described in this article: Diagnose Firefox issues using Troubleshoot Mode?

Thanks for the suggestions. Restarting FF 15.0.1 with all add-ons disabled seems to work ! I wonder why FF behaves in this way - surely a flaw there ? Now let's see if it goes on working .... But for the moment I'm much happier than I was. So thanks again.