Something in my iceweasel configuration is causing images to break, and I don't want to lose my many years of carefully crafted configuration, so I'm removing add-ons one by one to determine what is causing this.
I though this would be a good opportunity to list my favorite add-ons.
- Flashblock -- Indispensable!
 - Webdeveloper
 - Torbutton -- Very handy for quick proxy switching.
 - Greasemonkey
 - Noscript
 - Javascript Options
 - Firebug -- I don't leave this one active as it's got some speed issues, but it's very handy.
 - Yslow -- See above.
 - Fasterfox -- Not sure this is needed anymore, but it was great for early versions.
 - Ebay toolbar -- Nicer 3rd party ebay toolbar.
 - Tamper Data -- I have use this to play tricks on web sites :) Good for security testing.
 - Bugmenot -- Auto-fills forms for annoying forced-registration websites.
 - Live HTTP Headers -- Unfortunately the current release does not work in FF3. I love seeing the Server: header in my status bar for every page I visit.
 - Header monitor
 - Adblock Filterset G Updater -- Keeps adblock updated.
 - Adblock plus
 - itsalltext -- Edit html textareas in a real editor!
 
It turned out Torbutton was the culprit. Kind of surprising considering it was in the "tor off" state when it was causing the image bug.
tech
