User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; hu-HU; rv:1.7.6) Gecko/20050223 Firefox/1.0.1 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; hu-HU; rv:1.7.6) Gecko/20050223 Firefox/1.0.1 In the page http://evilboris.greg2k.com/cotton/bmchars.html there are several images using old-school transparency faking. This method to simulate half-transparent images works by having one pixel with full opacity followed by one pixel with zero opacity. This is almost impossible to notice on high resolutions as the pixels almost "blend" together, creating a nice faked transparency effect. Many old console games indeed used this method to fake transparency effects on the limited hardware available at the time, infact the images themselves are from such an old console game. (note: if you do not understand my explanation, please open the character portrait picture on the left side of the page in an image editor and enlarge them to see what I mean. English is not my main language, and I can't explain it any better, sorry about this.) In Firefox, pictures using this faking method take a lot of CPU time to render, making the site display very slowly. This is the most noticable when scrolling the page. Although its true that the page is not W3C valid, and uses some other things that can hit the performance of the browser (overuse of tables, still background images, etc.), The various other parts of the site you can visit from http://evilboris.greg2k.com/cotton/ also use the same elements while maintaining a steady and fast rendering speed with absolutely no noticable slowdown. So, it's most likely a bug in the image rendering engine of Firefox and browsers using the same engine. Also, even with the removal of said elements that could cause slowdown, the pictures using the faked transparency will still slow down the scrolling. In Microsoft Internet Explorer 6, this bug does not happen. I have not tested it on other browsers, people did reported the same bug on Netscape however. I also have not tested it under different OS, only Windows XP. Reproducible: Always Steps to Reproduce: 1. Create an image with the above explained "fake transparency" in it, and put some of them on a webpage, most likely on a webpage that is big enough to require scrolling it. 2. View the page and see that it renders very slowly. 3. If the effect is not noticable, try adding several of the same images to the page and check it again. Actual Results: The problem explained in the details. Expected Results: The software should have rendered the pages without any, or at least very minimal speed loss. My computer is an Athlon XP+ running at 2100Mhz with a Geforce 4 MX video card, with the display set to 1152x768 in 32bpp mode with 85Hz monitor refresh rate. This is more then enough to render the page at correct speed in Firefox, as it does in Internet Explorer 6.

*** This bug has been marked as a duplicate of 64401 ***