After viewing pdfs and exiting, Firefox hangs and thrashes to disk

Question

I'm using v3.6.13 on Windows XP64. When I have opened pdf files using Acrobat within the browser window and then close Firefox, firefox.exe remains in Task Manager and (loudly and annoyingly) thrashes to disk for many minutes. The only way to stop the disk access is to kill the firefox.exe process. This is easy to duplicate - Firefox closes normally (albeit with the delay others have noticed) if I have not viewed any pdf files, but hangs on exit regularly after pdfs have been opened.

Answer 1

Here is the new troubleshooting information, if it helps.
Application Basics
Name: Firefox
Version: 24.0
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:24.0) Gecko/20100101 Firefox/24.0
Extensions
Important Modified Preferences
browser.cache.disk.capacity: 358400
browser.cache.disk.smart_size_cached_value: 358400
browser.cache.disk.smart_size.first_run: false
browser.cache.disk.smart_size.use_old_max: false
browser.startup.homepage_override.buildID: 20130910160258
browser.startup.homepage_override.mstone: 24.0
extensions.lastAppVersion: 24.0
gfx.blacklist.webgl.msaa: 4
network.cookie.prefsMigrated: true
plugin.importedState: true
plugin.state.silverlight: 0
privacy.sanitize.migrateFx3Prefs: true
Graphics
Device ID: 0x 655
GPU Accelerated Windows: 1/1 OpenGL
Vendor ID: 0x10de
WebGL Renderer: NVIDIA Corporation -- NVIDIA GeForce GT 120 OpenGL Engine
windowLayerManagerRemote: false
AzureCanvasBackend: quartz
AzureContentBackend: none
AzureFallbackCanvasBackend: none
JavaScript
Incremental GC: true
Accessibility
Activated: false
Prevent Accessibility: 0
Library Versions
NSPR
Expected minimum version: 4.10
Version in use: 4.10
NSS
Expected minimum version: 3.15.1 Basic ECC
Version in use: 3.15.1 Basic ECC
NSSSMIME
Expected minimum version: 3.15.1 Basic ECC
Version in use: 3.15.1 Basic ECC
NSSSSL
Expected minimum version: 3.15.1 Basic ECC
Version in use: 3.15.1 Basic ECC
NSSUTIL
Expected minimum version: 3.15.1
Version in use: 3.15.1