User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.8.0.1) Gecko/20060111 Firefox/1.5.0.1 Build Identifier: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.8.0.1) Gecko/20060111 Firefox/1.5.0.1 When attempting to open many (10-15) tabs at once, Firefox becomes very sluggish in responding to UI events (clicking on a different tab, for example, or clicking "stop loading" or the close-tab X). Reproducible: Always Steps to Reproduce: 1. Create a bookmark folder with ~15 bookmarks that take a significant amount of time to load. A set of web comics (e.g., www.ucomics.com) is an excellent test case. 2. Choose "open in tabs" for that folder 3. Try to interact with the application while the pages load: click on another tab, try to close a tab, try to switch to another open window, etc. Actual Results: Response is slow. Application shows spinning-pizza activity cursor some of the time. Spinning activity indicators on tabs remain still (don't update). Expected Results: Responsiveness should be better. Try the exact same set of bookmarks in Safari for comparison.

Maybe related to Suite bug 216358 comment 2 -> Core bug 238935?

I can see this problem on Windows, on every version of Firefox. Can somebody confirm on Linux? Then I can update the HW and OS fields. I am not sure about the duplicate, the comments there say it becomes better. My experience is about the same (it becomes better only due to gecko speedups).

You can also make this happen more often if you're on a slow net connection. Background tabs that are waiting to talk to DNS or web servers can cause the foreground tab to hang / act sluggish.

aceman, Pam, I think this is much improved in current versions. Do you agree, or disagree?

It is better with many small sites loading. But the testcase in bug 595574 is still bad. I understand this is a known problem that electrolysis is aiming to fix. This bug is quite old, I have since changed hardware so I can't really compare. I'd agree with the duplicate.