User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E) Build Identifier: When I have these three web pages open in FF 3.6 (three tabs containing the documents each), Firefox hangs while reading the second page: https://wiki.mozilla.org/Evangelism/Firefox3.5/35Days/Articles/Defer_on_script_elements https://developer.mozilla.org/En/HTML/Element/Script http://www.whatwg.org/specs/web-apps/current-work/#script Reproducible: Always Steps to Reproduce: 1. Open above three web pages, each in a different tab 2. Read/scroll through the second document 3. Aber approx. 10-30 seconds, Firefox hangs Please note: I don't have any plug-ins installed or downloaded other than those coming with Firefox originally. Actual Results: Firefox hangs Expected Results: Firefox should flawlessly display these pages.

I now know that it's just the third URL that's getting Firefox hang. It's because of its huge size. However, Firefox should not stall when loading large HTML files. It should continue to be responsive as usual.

Verified. This is fixed on trunk.

Removed Duplicate flag due to discussion at bug 481131.

The reported hang was fixed in bug 526394. The general issue of "browser UI should not freeze up when a webpage does" is covered by existing bugs and the electrolysis work.