This could be because an installed add-on is forcing Firefox to remain open.

In order to be able to find the correct solution to your problem, we require some more non-personal information from you. Please do the following:

• Click the Firefox button at the top left, then click the Help menu and select Troubleshooting Information from the submenu. If you don't have a Firefox button, click the Help menu at the top and select Troubleshooting Information from the menu.

Now, a new tab containing your troubleshooting information should open.

• At the top of the page, you should see a button that says "Copy text to clipboard". Click it.
• Now, go back to your forum post and click inside the reply box. Press Ctrl+V to paste all the information you copied into the forum post.

If you need further information about the Troubleshooting information page, please read the article Use the Troubleshooting Information page to help fix Firefox issues.

Thanks in advance for your help!

Same problem here. And I'm running OS X Mavericks, too. Here's my clipboard info:

Application Basics

Name: Firefox Version: 26.0 User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:26.0) Gecko/20100101 Firefox/26.0

Extensions

Name: Copy URL Version: 1.2.4 Enabled: true ID: jid0-ZAHxU5e9sjK6VVQ8uP9TqpnlWuk@jetpack

Name: Favicon Restorer Version: 1.4 Enabled: true ID: faviconrestorer@masserog.it

Name: FireFTP Version: 2.0.17 Enabled: true ID: {a7c6cf7f-112c-4500-a7ea-39801a327e5f}

Name: Hide Tab Bar With One Tab Version: 1.2beta3 Enabled: true ID: {e5bbc237-c99b-4ced-a061-0be27703295f}

Name: keyconfig Version: 20110522 Enabled: true ID: keyconfig@dorando

Name: Remove New Tab Button Version: 1.0 Enabled: true ID: remove-new-tab-button@forerunnerdesigns.com

Name: Status-4-Evar Version: 2013.10.31.22 Enabled: true ID: status4evar@caligonstudios.com

Name: Universal Print Version: 0.4.25 Enabled: true ID: {BE2100B3-1D80-48eb-ACCF-D26750644378}

Name: Adobe Acrobat - Create PDF Version: 2.0 Enabled: false ID: web2pdfextension@web2pdf.adobedotcom

Important Modified Preferences

accessibility.browsewithcaret: true accessibility.typeaheadfind.flashBar: 0 accessibility.warn_on_browsewithcaret: false 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.places.smartBookmarksVersion: 4 browser.privatebrowsing.autostart: true browser.sessionstore.restore_on_demand: false browser.sessionstore.upgradeBackup.latestBuildID: 20131205075310 browser.startup.homepage: http://webvantage.mastermindsagency.com/SignIn.aspx?ReturnUrl=%2f browser.startup.homepage_override.buildID: 20131205075310 browser.startup.homepage_override.mstone: 26.0 browser.tabs.autoHide: true browser.tabs.onTop: false browser.tabs.warnOnClose: false browser.tabs.warnOnOpen: false dom.max_script_run_time: 0 dom.mozApps.used: true dom.w3c_touch_events.expose: false extensions.lastAppVersion: 26.0 font.default.x-western: sans-serif font.internaluseonly.changed: false font.name.sans-serif.x-western: Lucida Grande font.name.serif.x-western: Lucida Grande font.size.fixed.x-western: 15 font.size.variable.x-western: 14 gfx.blacklist.direct2d: 3 gfx.blacklist.layers.direct3d9: 3 network.cookie.prefsMigrated: true network.dns.disableIPv6: true network.http.max-persistent-connections-per-proxy: 10 network.http.max-persistent-connections-per-server: 10 network.http.pipelining: true network.http.pipelining.maxrequests: 30 network.http.pipelining.ssl: true network.http.proxy.pipelining: true places.database.lastMaintenance: 1389801392 places.history.expiration.transient_current_max_pages: 104858 places.history.expiration.transient_optimal_database_size: 167772160 plugin.disable_full_page_plugin_for_types: application/pdf plugin.importedState: true plugin.state.adobepdfviewernpapi: 0 plugin.state.citrixonlinewebdeploymentplugin: 0 plugin.state.directorshockwave: 0 plugin.state.flip4mac wmv plugin: 0 plugin.state.ovshelper: 0 plugin.state.sharepointbrowserplugin: 0 plugin.state.yahoo! installer: 0 print.macosx.pagesetup-2: PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPCFET0NUWVBFIHBsaXN0IFBVQkxJQyAiLS8vQXBwbGUvL0RURCBQTElTVCAxLjAvL0VO print.print_bgcolor: false print.print_bgimages: false print.print_colorspace: print.print_command: print.print_downloadfonts: false print.print_duplex: 402653184 print.print_evenpages: true print.print_in_color: true print.print_margin_bottom: 0.5 print.print_margin_left: 0.5 print.print_margin_right: 0.5 print.print_margin_top: 0.5 print.print_oddpages: true print.print_orientation: 0 print.print_page_delay: 50 print.print_paper_data: 0 print.print_paper_height: 11.00 print.print_paper_name: print.print_paper_size_type: 1 print.print_paper_size_unit: 0 print.print_paper_width: 8.50 print.print_plex_name: print.print_resolution: 32767 print.print_resolution_name: print.print_reversed: false print.print_scaling: 1.00 print.print_shrink_to_fit: true print.print_to_file: false print.print_unwriteable_margin_bottom: 0 print.print_unwriteable_margin_left: 0 print.print_unwriteable_margin_right: 0 print.print_unwriteable_margin_top: 0 privacy.cpd.offlineApps: true privacy.cpd.siteSettings: true privacy.donottrackheader.enabled: true privacy.popups.showBrowserMessage: false privacy.sanitize.migrateFx3Prefs: true security.warn_viewing_mixed: false storage.vacuum.last.index: 1 storage.vacuum.last.places.sqlite: 1388067686

Graphics

Device ID: 0x6720 GPU Accelerated Windows: 2/2 OpenGL (OMTC) Vendor ID: 0x1002 WebGL Renderer: ATI Technologies Inc. -- ATI Radeon HD 6970M OpenGL Engine windowLayerManagerRemote: true AzureCanvasBackend: quartz AzureContentBackend: quartz AzureFallbackCanvasBackend: none AzureSkiaAccelerated: 0

JavaScript

Incremental GC: true

Accessibility

Activated: false Prevent Accessibility: 0

Library Versions

NSPR Expected minimum version: 4.10.2 Version in use: 4.10.2

NSS Expected minimum version: 3.15.3.1 Basic ECC Version in use: 3.15.3.1 Basic ECC

NSSSMIME Expected minimum version: 3.15.3.1 Basic ECC Version in use: 3.15.3.1 Basic ECC

NSSSSL Expected minimum version: 3.15.3.1 Basic ECC Version in use: 3.15.3.1 Basic ECC

NSSUTIL Expected minimum version: 3.15.3.1 Version in use: 3.15.3.1

Plugins are usually a more likely cause for such hangs.

See also:

• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs
• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs