User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0) Gecko/20121210 Firefox/19.0 Build ID: 20121210042017 Steps to reproduce: I visited threads on http://boards.4chan.org/g/ using this greasemonkey extension http://userscripts.org/scripts/show/153485 which downscales every image and uses them as thumbnails. Actual results: Half the time, maybe less, the old algorithm is in effect, on random thumbnails around the page. Refreshing the page often fixes it. Expected results: The new algorithm should have been used.

Here is what the page looked like when I refreshed it: http://img853.imageshack.us/img853/6886/euoaoeueu.png Note the change in the quality of the thumbnails. I should also make it clear that this was not an isolated occurrence.

Please don't use Imageshack, they resize images and it's horrible to watch. Use http://imgur.com/ or attach the screenshot to the bug report, thanks.

Comment on attachment 690907 [details] Here is the page when I refreshed it. Note the change in the quality of the thumbnails. Sometimes a refresh fixes it. Sometimes it doesn't. Sometimes changing the min factor to -999999, 0, 999999, or something else fixes it, but that will break other images, the min factor doesn't really seem to have a pattern…

Do you have better steps to reproduce like a link to test repeatedly the script? (4chan is moving too fast) Do I need to configure the script after installing it in Greasemonkey?

(In reply to Loic from comment #6) > Do you have better steps to reproduce like a link to test repeatedly the > script? (4chan is moving too fast) The best I can give you is to go to either https://boards.4chan.org/w/ or https://boards.4chan.org/wg/ Those are wallpaper boards, so they are always full of image posts. > Do I need to configure the script after installing it in Greasemonkey? No; the important settings are the “quality thumbnail” settings, and those are enabled by default.

What do the "old algorithm" and "new algorithm" parts of comment 0 refer to?

(In reply to Boris Zbarsky (:bz) from comment #8) > What do the "old algorithm" and "new algorithm" parts of comment 0 refer to? The old downscaling algorithm and the new one of same.

Where are these algorithms? In the script? Or are you talking about the browser? If you're talking about the browser, I have no idea what you're talking about....

(In reply to Boris Zbarsky (:bz) from comment #10) > Where are these algorithms? Or are you talking about the > browser? If you're talking about the browser, I have no idea what you're > talking about.... Yes, the browser. Aurora has a new option: image.high_quality_downscaling.enabled. When it's in effect, a new resizing algorithm, like a bicubic or something, is used, when it is not used, the old, nearest neighbour, process is used instead. All the script does is just resizes a bunch of images, basically. The issue I'm having is with the browser. The browser does not always use the same algorithm to resize, even though my selection of behaviour is static. Specifically, it will sometimes not use the new algorithm over the old algorithm even though I have told it to use the new algorithm. That is to say that it the opposite is not true – I have not seen it using the new algorithm when that option is turned off.

OK. So the downscaling always happens, but sometimes it uses nearest-neighbor even though you have that preference set?

(In reply to Boris Zbarsky (:bz) from comment #12) > OK. So the downscaling always happens, but sometimes it uses > nearest-neighbor even though you have that preference set? Correct.

We have a known limitation of only one view of an image being allowed at a time. I heavily suspect that's what's happening here.