253613 - 100% CPU usage holding down tab key, no scrolling necessary

Status: RESOLVED FIXED

(Core :: DOM: Events, defect)

Description

[Aaron Cutchin]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7) Gecko/20040707 Firefox/0.8
Build Identifier: Firefox 0.9.2

Using Windows2000, SP4, Build 5.00.2195, Firefox 0.9.2

There appears to be a bug in Firefox with background images and tabbing through
hyperlinks.  I originally found this bug on zoneedit.com, but created a test
document on my server to demonstrate it.  My test document has a simple
background image using the style directive: "body { ... background: url(bg.gif);
... }".  The image is 50X20 pixels, palette/256-color, and transparent.

When you try to tab through hyperlinks in the page, CPU usage spikes to ~100%
and the focus moves extremely slowly.  This does not happen in IE.

It does not seem to matter if the image is plain white or has a design, or if it
is transparent or not.  HOWEVER, a 24-bit/true-color image of the same size and
design does not cause quite as much CPU usage.

I noticed a bug report about page scrolling causing 100% CPU in Firefox, but
thought this might be somewhat different because there is no scrolling involved.


Reproducible: Always
Steps to Reproduce:
1) Open task manager and minimize to the system tray.

2) Open http://www.aaron1.net/ff.bug/test.html in Internet Explorer.  (Or
http://www.zoneedit.com if that's offline.)  Hold down the TAB key and watch the
focus scroll through all the hyperlinks rapidly with little or no CPU usage.

3) Open same page in Firefox 0.9.2.  Hold down the TAB key and watch your CPU
usage spike to 100%.

Actual Results:  
100% CPU usage

Expected Results:  
minimal CPU usage

Comment 1

[Aaron Leventhal]

WFM Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8a3) Gecko/20040730
Firefox/0.9.1+

Comment 2

[Aaron Leventhal]

I take it back, I am seeing CPU at 100%. However, the processes list still says
"Mozilla 00" or "Mozilla 01".

Also, the special testcase and background image is not required. I get this
holding down tab in any page -- a bugzilla page will do. Resummarizing to
reflect that.

Comment 3

[Wayne Mery (:wsmwk)]

testcase http://www.zoneedit.com/ 
1. resize text to fit on screen so window doesn't scroll (just scrolling with mouse eats a lot of cpu)
2. tab

cpu maxes out. But tab is fast, not slow as mentioned by reporter
IE cpu is far lower, about 1/3 of FF

related to bug 307856?

aaron's testcase is gone http://www.aaron1.net/ff.bug/test.html

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9a3pre) Gecko/20070216 Minefield/3.0a3pre

Comment 4

[Aaron Cutchin]

In FF 2.0.0.1, CPU usage does not seem to be excessive when holding down the TAB key and scrolling through a page.  Seems to have been fixed sometime during the last 2.5 years!

closing.