When typing in GMail (firefox and thunderbird) keyboard randomly uses foreign characters like it has been set to another language, but setting is eng

Question

When typing in gmail (firefox) or thunderbird, randomly foreign characters will be produced like the keyboard has been set to spanish or french, but it is set to english, and the character encoding is set to what it is supposed to be. Web pages appear correctly.
Application Basics
Name
Firefox
Version
10.0.12
User Agent
Mozilla/5.0 (Windows NT 5.1; rv:10.0.12) Gecko/20100101 Firefox/10.0.12
Profile Directory
Open Containing Folder
Enabled Plugins
about:plugins
Build Configuration
about:buildconfig
Crash Reports
about:crashes
Memory Use
about:memory
Extensions
Name
Version
Enabled
ID
F5 Networks Host Plugin
7000.2011.0910.0354
true
{DBBB3167-6E81-400f-BBFD-BD8921726F52}
IE Tab 2 (FF 3.6+)
4.12.22.2
true
{1BC9BA34-1EED-42ca-A505-6D2F1A935BBB}
Microsoft .NET Framework Assistant
0.0.0
false
{20a82645-c095-46ed-80e3-08825760534b}
Skype Click to Call
6.5.0.11422
false
{82AF8DCA-6DE9-405D-BD5E-43525BDAD38A}
Modified Preferences
Name
Value
accessibility.typeaheadfind.flashBar
0
browser.places.smartBookmarksVersion
2
browser.startup.homepage
http://ca.search.yahoo.com?type=386496&fr=spigot-yhp-ff
browser.startup.homepage_override.buildID
20130103094221
browser.startup.homepage_override.mstone
rv:10.0.12
browser.tabs.warnOnClose
false
dom.ipc.plugins.enabled.npietab2.dll
true
extensions.lastAppVersion
10.0.12
gfx.blacklist.layers.direct3d9
2
keyword.URL
http://search.yahoo.com/search?fr=greentree_ff1&ei=utf-8&ilc=12&type=386496&p=
network.cookie.prefsMigrated
true
places.database.lastMaintenance
1358793548
places.history.expiration.transient_current_max_pages
51968
privacy.cpd.siteSettings
true
privacy.sanitize.migrateFx3Prefs
true
privacy.sanitize.timeSpan
0
security.warn_viewing_mixed
false
Graphics
Adapter Description
NVIDIA GeForce 6150 LE
Vendor ID
10de
Device ID
0241
Adapter RAM
Unknown
Adapter Drivers
nv4_disp
Driver Version
9.1.4.8
Driver Date
8-16-2006
Vendor ID (GPU #2)
00ad
Device ID (GPU #2)
00ad
Adapter RAM (GPU #2)
Unknown
Adapter Drivers (GPU #2)
Unknown
Driver Version (GPU #2)
2.1.3.0
Driver Date (GPU #2)
1-1-2007
WebGL Renderer
Google Inc. -- ANGLE (NVIDIA GeForce 6150 LE) -- OpenGL ES 2.0 (ANGLE 0.0.0.809)
GPU Accelerated Windows
0/1. Blocked for your graphics driver version.

Answer 1

It is possible that you have switched the keyboard layout by accident.
* http://support.microsoft.com/kb/258824 - How to change your keyboard layout
Windows remembers the keyboard layout setting per application and you may have changed the keyboard layout by accident via a keyboard shortcut.
* http://support.microsoft.com/kb/306993 - HOW TO: Use the Language Bar in Windows XP
* Make sure that you have the Language bar visible on the Windows Taskbar
* You can do that via the right-click context menu of the Taskbar: Toolbars > Language Bar
* Check the keyboard language (keyboard layout) setting for the application that has focus via the icon on the Language bar
* You need to do that while Firefox has focus because Windows remembers the keyboard layout setting per application
* The default key combination to rotate the layout is the Ctrl+Shift or Alt+Shift combination that Firefox uses for some menu items
* To avoid an unintentional switch, assign a specific key sequence (Alt/Ctrl+Shift+number) to select keyboard layouts and remove the key combination to rotate layouts (Alt+Shift or Ctrl+Shift)
* Control Panel > Regional and Language Options > Languages > Text services and input languages > Details > Key Settings > Change Key Sequence