649823 - FF4 tests true for javascript IE Filter support

Status: RESOLVED INVALID

(Core :: DOM: CSS Object Model, defect)

Description

[offworldgirl]

User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0
Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0

FF4 tests true in javascript feature query for IE CSS "filter" support.  This  breaks FF4 opacity effects.

Reproducible: Always

Steps to Reproduce:
1. if(typeof document.documentElement.style.filter === "string"){alert('IE Filter');}else{alert('Standards');}
2. Run javascript in a page
3. Observe which alert is triggered
Actual Results:  
Triggers alert "IE Filter" instead of "Standards"

Expected Results:  
It should show alert "Standards" since FF4 does not support IE "filter" method.

Workaround for now is to replace if-else with two if statements:

if (typeof document.documentElement.style.filter === "string"){
alert('IE Filter'); // FF4 should NOT grab this but does!
}
if (typeof document.documentElement.style.opacity === "string") {
alert('Standards'); // FF4 also grabs this so it can override filter
}

So FF4 grabs the first condition as true, then subsequently grabs the second condition as true too, so it can be used to override the erroneous "filter" method being used.

Comment 1

[Masatoshi Kimura [:emk]]

It's because SVG filter property is supported in HTML (bug 450340).

Comment 2

[Boris Zbarsky [:bzbarsky]]

Yep.  The assumption that "filter" is an IE-only property is just wrong.  We support .style.filter as required by SVG.  See bug 374216 for the details.