There must already be a bug for this, but I can't find it. And I mistakenly posted it to bug 27146 (it was late - I feel like a boob). I have been having a performance problem with mozilla. The problem I notice is that the layout processing can take so much of the CPU that network activity is starved. For instance, if I go to Slashdot there is an initial delay while the HTML page downloads. During this time the statusbar and the throbber are active. Then, once it has enough info to attempt layout the status bar animation and the throbber halt in midstream and the network activity stops at the same time. After a few seconds (depending on page complexity and speed of my machine) mozilla presents the layout and then begins downloading inlined images. Now, IMHO this is definately bad behaviour. For those of us on dialup connections, downloading images is the top delay in web browsing. The network code should never be starved of processing time. The layout should be processed a little slower rather than delaying download of the inline images for 2-3 seconds.

Forgot to mention I have noticed this for a while, most recently on the 2/28 build. I can't remember when it started but I think it was sometime after M13.

The networking code runs in a separate thread so it isn't getting srarved. What you're seeing is the UI being unresponsive layout while part of the page is being formatted

Not being intimate with the code, I'll take your word about the seperate thread thing. However, it is not just UI unresponsiveness. That would explain why the animated GIFs temporarily stop spinning, but it does not account for why the SX and RX lights on the modem go dark for the period of time that mozilla is working on the layout. Mozilla should know what other dependencies it needs (inline images etc.) and it should be retrieving them constantly. Instead it always ceases newtwork activity for the period of time that mozilla starts churning on the layout. Now that just sounded like starvation to me, but there is some problem somewhere.

Marking this as a DUP of 17325. It's the same issue of content sink notifications *** This bug has been marked as a duplicate of 17325 ***

Marking verified dup of 17325.