Comment 216 for bug 182038

I have originally reported this but after adding the XaaNoOffscreenPixmaps or whatever option to xorg.conf I could no longer reproduce. Actually my Linux machine broke since so now I am unable to test.

But maybe there are multiple unrelated bugs. There is definitely the progressively loading image disappearing after being loaded.
But if you look closely you can see parts of other non-firefox windows appear in the image as it loads, of course the pixels are offset but try opening a window with a distinctive uniform color and you will see that color appear. That really hints at an X bug.
There doesn't need to be an alpha channel at least I also got the same effect with old frames in animated GIFs being replaced by noise/other windows' contents/blank whiteness.

One thing that could by done is trying to reproduce with various builds between firefox 2 and now and see where it appears first and look at what changes happened then. Once I got Linux again I will try.

What I think happens is that X gives a buffer to firefox, it's memory has of course been previously used so it may contain other windows. Then firefox adds some parts of the loading image. In firefox 2 this buffer contained the previously decoded parts of the image but now it's a new buffer. How this happens I don't know yet. But every part of the image is decoded correctly just not put together right.
Firefox/Gecko uses server side images for speed while most other apps don't so they don't expose this issue.

For the record I didn't have any extensions or plugins and also didn't use compiz.

I could reopen or change the title but I don't know what to..