890445 - Firefox fails to pass Acid2 when system font size is not 100%

Status: RESOLVED DUPLICATE of bug 418235

(Firefox :: Untriaged, defect)

Description

[T.Rosenau]

Attachment: turtle.png

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:22.0) Gecko/20100101 Firefox/22.0 (Beta/Release)
Build ID: 20130618035212

Steps to reproduce:

1. Set your system font size to 125%, for example.
2. Take the Acid2 test http://www.webstandards.org/files/acid2/test.html#top

Alternatively, manually change layout.css.devPixelsPerPx in about:config to simulate step 1.
Note that the Acid2 test requires "When taking the test, you should use the default settings of the browser you are testing.", and the default value is layout.css.devPixelsPerPx=-1. Thus, Firefox inherits the system's font size, which on HD screens may default to 1.25.


Actual results:

We see a Teenage Mutant Ninja Turtle (cf. attachment)

Apparently, there's something wrong with the background-image of div#eyes-b

Comment 1

[T.Rosenau]

I haven't really digged into this, but it may have the same cause as Bug 890383, and may be related to Bug 820679.

Comment 2

[Greg Edwards]

Dupe of Bug 418235.
Firefox's use of bilinear upscaling (or just about any other algorithm besides nearest) causes stacked alpha composition which isn't 100% opaque, causing the test to not render as expected. The W3C allows the UA to choose which algorithm to upscale images with, so Firefox is working as designed.

tl;dr: it's a bug in the test, not Firefox.