262028 - slow selection on site with unqualified :active rule

Status: NEW

(Core :: CSS Parsing and Computation, defect)

Description

[Sekundes]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8a4) Gecko/20040927
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8a4) Gecko/20040927

It works well on 1.7.3.

Reproducible: Always
Steps to Reproduce:
1. Hightlight the sentenece named "Fahrenheit 1 Million: The temp at which the
web explodes" to the whole post.
2. It makes very slow selection on 1.8a4.

Comment 1

[Boris Zbarsky [:bzbarsky]]

The problem is that the site has the following style rule:

  :active { 
    color: #000; 
  }

in http://www.spreadfirefox.com/themes/phptemplate/spreadfirefox/style.css

In 1.7.x this rule doesn't do much, but in current builds, with hierarchical
:active, this means that that clicking anywhere in the document affects the
style of the root element.  So any click will cause a full style reresolve on
the root (and hence on all nodes in the document).  I did a profile of doing a
bunch of selecting and unselecting and of the 232003 total hits, 219841 were
under ProcessPendingRestyles...

I'm not really sure what we can do to improve this, other than simply fixing the
CSS to not be silly, of course.  I've filed bug 262839 on that.