I used to get a warning when receiving my Yahoo calendar with OE6, so I used the custom email settings to remove checking for remote iFrames, and the problem was solved. Now, in a new installation of WinXP SP2 with all updates, and Thunderbird 1.5 RC2, I no longer get the warning even with the remote iFrame check enabled, it just filters out the images from the email. When I again remove checking for the remote iFrames, the Yahoo mail is displayed correctly (with HTML and images). I am using avast! 4.6.744 in a clean installation, and am not using Silent Mode.
Since I don’t filter the remote iFrame anyway, the lack of a warning is not a problem for me, but it could be for someone else. Is it due to Thunderbird or something else? (I also use Firefox 1.5 now, instead of IE 6).