Tested with build 2001072503 on Win2k (SP2) This testcase is taken off of bug 66022 which was morphed to a crasher bug. The crash is now fixed, but jst didn't want to reopen that bug for anything but a crash, hence this bug. Shortly, I'm attaching attaching a testcase which is identical to the on in the URL field, except that -moz-opacity is initialized to 99.999996% rather than 100%. The testcase in the URL bar does *not* work, whereas the modified testcase *does* work. Expected resluts when running testcases: Image should slowly disappear in both testcases Actual: Image only disappears in the modified testcase with -moz-opacity initially set to 99.999996% jake

changing platform to "all" based on setting for bug 66022 Sorry for the spam. Jake

hm... the opacity value is reset as desired. It's just that the image's display does not correspond to its opacity value... Compositor bug?

Not sure if this helps any more, but it looks like the upper limit is very specifically: 99.9999961853% Jake

Yes, it's a Compositor bug. It explains bug 58501 and part of bug 57307.

Can anyone actually tell me how opacity works so I can figure out why it doesn't work for OS/2?

*** This bug has been marked as a duplicate of 33601 ***