Why or how could firefox change my proxy settings without me doing anything right in the middle of browsing the internet?

Question

== Issue
==
I have another kind of problem with Firefox
== Description
==
While I was browsing the internet suddenly nothing would happen when I clicked a link. Upon closing and opening firefox and trying to load a web page it said "the proxy server is refusing connection. Firefox is configured to use a proxy server that is refusing connections."
I did manage to fix the problem by changing the proxy settings from manual to auto-detect but what disturbs me is how those settings could be changed without me doing so right in the middle of using the internet. I dont know if its a bug or a security issue but I thought I would let you guys know.
== This happened
==
Just once or twice
== In the middle of browsing the Internet
==
== Troubleshooting information
==
Application Basics
Name Firefox
Version 3.6.7
Profile Directory
Open Containing Folder
Installed Plugins
about:plugins
Build Configuration
about:buildconfig
Extensions
Name
Version
Enabled
ID
Exif Viewer 1.55 true [email protected]
Java Console 6.0.18 false
Java Quick Starter 1.0 false [email protected]
Microsoft .NET Framework Assistant 1.1 true {20a82645-c095-46ed-80e3-08825760534b}
FiddlerHook 2.2.8.2 false [email protected]
Torbutton 1.2.5 true
Modified Preferences
Name
Value
accessibility.typeaheadfind.flashBar 0
browser.places.importBookmarksHTML false
browser.places.smartBookmarksVersion 2
browser.startup.homepage www.google.ca
browser.startup.homepage_override.mstone rv:1.9.2.7
browser.tabs.warnOnClose false
extensions.lastAppVersion 3.6.7
general.useragent.extra.microsoftdotnet (.NET CLR 3.5.30729)
network.cookie.prefsMigrated true
network.security.ports.banned 8118,8123,9050,9051
places.last_vacuum 1279480436
privacy.cpd.cookies false
privacy.cpd.sessions false
privacy.sanitize.migrateFx3Prefs true
privacy.sanitize.timeSpan 0
security.warn_viewing_mixed false
== Firefox version
==
3.6.7
== Operating system
==
Windows XP
== User Agent
==
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.7) Gecko/20100713 Firefox/3.6.7 (.NET CLR 3.5.30729)
== Plugins installed
==
*-Adobe PDF Plug-In For Firefox and Netscape
*Default Plug-in
*Shockwave Flash 10.0 r42
*Windows Presentation Foundation (WPF) plug-in for Mozilla browsers
*Next Generation Java Plug-in 1.6.0_18 for Mozilla browsers
*Npdsplay dll
*DRM Store Netscape Plugin
*DRM Netscape Network Object

Answer 1

Calvin W.:
Your extensions list shows an enabled "Torbutton 1.2.5" extension, so it is possible that that extension is responsible for that change.