Try this instead:

• Download the full Firefox installer and save the file to the desktop
  http://www.mozilla.org/en-US/firefox/all.html
• Start the installation with a double-click on the desktop icon

Sadly I have already tried this with no result.

whats more, Mozilla now regularly crashes, usually in the middle of something.

When you download the Firefox install from cor-el's link, try to right click and run as Administrator to see if it installs. Does that get it installed?

As for your crashes, Can you give us your crash reports?

1. Enter about:crashes in the Firefox address bar and press Enter. A Submitted Crash Reports list will appear, similar to the one shown below.
2. Copy the 5 most recent Report IDs that start with bp- and paste them into your response here.

Date Submitted fb61e8d4-9edf-4c78-8d10-f3f20120de2f 3/06/2014 3:40 AM c1631ac6-ef3d-4bce-a2c4-245b882c2f52 1/06/2014 1:25 AM d9e3621e-62ba-4a34-abd6-2c3766d148b4 31/05/2014 1:34 PM 365d87d6-ac10-492f-bece-150add64463d 31/05/2014 6:26 AM 455c4e14-9f3d-45b0-a902-b259d39ad430 30/05/2014 8:06 PM 5a473c42-dfb6-4a95-b515-87c641c57768 30/05/2014 6:25 AM 92bf9a6e-99fb-4dc2-8e98-a2dec73acc6e 16/05/2014 6:56 AM bp-759b00ba-c2a4-4258-b9b0-4a3902140515 16/05/2014 6:51 AM d2beb6cb-f5dd-468c-8f9e-f518c2e53b6e 12/05/2014 10:07 AM 8449d4c6-6b5a-4d60-a4ce-1532419464b7 10/05/2014 2:30 PM bp-b1d02f79-b29a-408d-ac0c-a7b032140508 8/05/2014 6:58 PM 37647c01-b57c-4d6d-ace2-ca721794e308 5/05/2014 12:30 PM 26b6362c-e684-4b2b-910e-43eb13f961ab 27/04/2014 1:50 PM bp-81ad3fc9-fcd7-4d80-8c53-bbc692140424 24/04/2014 6:09 PM bp-88797ac9-89b3-462d-af49-f69532140424 24/04/2014 10:48 AM bp-fa974c25-ec84-4d7c-96e7-85bf72140417 17/04/2014 11:58 AM bp-2a4c7106-bf20-4c59-8f06-255e02140414 14/04/2014 6:43 PM

From my second computer

bp-64abcc31-2fb7-4844-a473-306f72140529 29/05/2014 1:49 PM 3585b6bd-8462-4a88-bd14-00ee8abf81d4 2/05/2014 11:58 PM cb2a3881-43ea-4c6b-9201-0e7b4cd55f7d 14/04/2014 6:49 PM bp-76472709-3a84-44c5-a5f2-8f8a22140405 6/04/2014 9:41 AM bp-b23dc14d-ebc4-406c-8399-588962140405 5/04/2014 3:34 PM bp-0a545783-3c7c-42df-be12-37bdf2140401 1/04/2014 4:12 PM 52eed6a9-7c70-4680-a0ac-58486748e1c6 21/03/2014 8:55 AM bp-b7d1ae59-d764-4cce-a687-10fa12140128 28/01/2014 10:47 AM d7dd67fe-2349-4c9f-a3da-59472ff79987 22/12/2013 9:49 AM 3de1e622-cb51-4ce9-acfa-b05777042656 11/12/2013 7:28 AM bc325fe6-2d60-48ab-af0d-05f62c7fe4ca 20/11/2013 2:42 PM 5720be9f-fae1-412d-8460-370c03b057ab 5/11/2013 11:03 AM 7327f1e2-e91c-42f2-a2de-287c3bf9775a 28/10/2013 5:31 PM fa2645e1-06cf-4dd8-8ddc-6d1310e6c843 21/10/2013 9:15 AM a76475a8-11da-4750-82d4-ca3a90509aee 6/10/2013 12:44 PM b18311db-1652-4255-8630-f77414d72a00 17/09/2013 11:32 AM 2b2fff0b-4612-4061-9a49-b4773ce20019 13/09/2013 10:04 AM bp-9cf5a3ee-e902-49cc-8a65-1c39a2130817 17/08/2013 5:38 PM 734b8780-fe47-4908-b85d-ce7f5ffdd5e5 30/07/2013 2:04 PM

Also have this problem

OK, so no answers then?

Now Firefox crashes about every five minutes.

Grrrrrrreat.

Still no joy in installing updated FF.

Not only that, and constantly crashing but now refuses to install anything as it cannot install a temp folder.

FF has now lost me. Cant get it to work. Cant get help.

Like so many others FF doesn't seem to care.

Please note that this forum is largely staffed by volunteers, and you didn't start posting more information until around 10PM here in Pacific time in the US.

Have you tried making sure your Computer is fully up to date? Scanning for malware? Troubleshoot Firefox issues caused by malware

Also, when you try to install Firefox, what error message does it give?