User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:25.0) Gecko/20100101 Firefox/25.0 (Beta/Release) Build ID: 20131028112446 Steps to reproduce: Fresh install of Ubuntu 13.10, 64-bit. Comes with Firefox. This issue affects both the Firefox version that came with it, and version 25.0 that it updated to a few days later. But I have also had this problem with all Firefox versions on Ubuntu for at least 6 months. At some point during Firefox use, spellcheck language reverts to UK or Canadian English even though I set it to en-US. I have set it with the right-click (context) menu, and I have set it by going to about:config and setting the spellchecker.dictionary setting to en-US. The problem still comes back. Actual results: Spellcheck language spontaneously changes itself to English (United Kingdom) or English (Canada). This happens very frequently, usually several times a week. Sometimes I have seen it happen more than once in 24 hours. I use the right-click context menu in any spellchecked text entry box to change it back to English (United States), and the first time, my setting fails to be set. I use the right-click context menu a second time and see that it didn't "stick" the first time so I set it to English (United States) again and now the setting works and I no longer see incorrect spellings detected for US vs. UK or CA spellings of English words. But the setting does not stay! It always works for the duration of my current session. But some time later, anywhere from the same day to a week later, I find that the spellcheck language has returned to en-UK or en-CA once again. This is very frustrating and has been going on for a long time. I reset my profile and that didn't change anything. Is it possible that Sync is keeping me stuck with the problem even after I reset? The fact that this happens with a fresh install of Firefox included with a fresh install of Ubuntu makes me think it's a bug and not just a problem with my prefs or profile. But the possibility of Sync affecting this makes me uncertain. Expected results: The setting should stay set properly and it should never change unless the user explicitly changes it. Nothing else should be able to override the user's choice of spellcheck language. Especially not repeatedly and with no warning.

Troubleshooting info cut and paste: You will see that I have some addons, but I have disabled them except for the Ubuntu integration stuff. Application Basics ------------------ Name: Firefox Version: 25.0 User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:25.0) Gecko/20100101 Firefox/25.0 Extensions ---------- Name: Ubuntu Firefox Modifications Version: 2.8 Enabled: true ID: ubufox@ubuntu.com Name: Ubuntu Online Accounts Version: 0.5 Enabled: true ID: online-accounts@lists.launchpad.net Name: Unity Desktop Integration Version: 2.4.8 Enabled: true ID: webapps-team@lists.launchpad.net Name: Unity Websites integration Version: 2013.09.20.beta Enabled: true ID: {2e1445b0-2682-11e1-bfc2-0800200c9a66} Name: Firebug Version: 1.12.4 Enabled: false ID: firebug@software.joehewitt.com Name: Stylish Version: 1.3.3 Enabled: false ID: {46551EC9-40F0-4e47-8E18-8E5CF550CFB8} Name: Web Developer Version: 1.2.5 Enabled: false ID: {c45c406e-ab73-11d8-be73-000a95be3b12} Important Modified Preferences ------------------------------ accessibility.typeaheadfind.flashBar: 0 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.sessionstore.upgradeBackup.latestBuildID: 20131028112446 browser.startup.homepage: about:home browser.startup.homepage_override.buildID: 20131028112446 browser.startup.homepage_override.mstone: 25.0 extensions.lastAppVersion: 25.0 font.default.x-western: sans-serif font.minimum-size.x-western: 12 font.name.monospace.x-western: Inconsolata font.name.sans-serif.x-western: DejaVu Sans font.name.serif.x-western: DejaVu Serif network.cookie.prefsMigrated: true places.database.lastMaintenance: 1383074715 places.history.expiration.transient_current_max_pages: 104858 plugin.disable_full_page_plugin_for_types: application/pdf plugin.importedState: true privacy.sanitize.migrateFx3Prefs: true storage.vacuum.last.index: 1 storage.vacuum.last.places.sqlite: 1382412413 Graphics -------- Adapter Description: X.Org -- Gallium 0.4 on AMD RV770 Device ID: Gallium 0.4 on AMD RV770 Driver Version: 3.0 Mesa 9.2.1 GPU Accelerated Windows: 0/1 Basic Vendor ID: X.Org WebGL Renderer: X.Org -- Gallium 0.4 on AMD RV770 windowLayerManagerRemote: false AzureCanvasBackend: cairo AzureContentBackend: none AzureFallbackCanvasBackend: none AzureSkiaAccelerated: 0 JavaScript ---------- Incremental GC: true Accessibility ------------- Activated: false Prevent Accessibility: 0 Library Versions ---------------- NSPR Expected minimum version: 4.10.1 Version in use: 4.10.1 NSS Expected minimum version: 3.15.2 Basic ECC Version in use: 3.15.2 Basic ECC NSSSMIME Expected minimum version: 3.15.2 Basic ECC Version in use: 3.15.2 Basic ECC NSSSSL Expected minimum version: 3.15.2 Basic ECC Version in use: 3.15.2 Basic ECC NSSUTIL Expected minimum version: 3.15.2 Version in use: 3.15.2

Similar to bug 858666.

This is happening to me as well; it seems to be related to enteing text on Facebook. See this archived thread: https://support.mozilla.org/en-US/questions/965624 I am using aurora on Arch Linux but had similar problems on various FF versions on my old computer, which ran Ubuntu 12.04, 12.10, and 13.04 preleases. FF versions went from about 24 to 27; currently using aurora just a few days old.

some other possible dupes: bug 853970 (almost certainly) bug 717433 (possibly) bug 728069 (maybe) bug 858666 (also referenced above)

Closing this bug as per bug 1073827, comment #33. If you want to reopen it, please present a reproducible test case.