1 Bug in

1- Computed css width and offsetWidth of a border-collapse: collapse table are wrong. Go to complete testcase (will open in the same window)

Specific Mozilla and Firefox bug collection sites

CSS 1 bugs in Gecko
Mozilla bugs at Peter-Paul Koch site
Firefox CSS 2.1 test failures by Robert Blaut
Voluntary Product Accessibility Template for Firefox 2 by Mozilla organization, October 2006
Voluntary Product Accessibility Template for Firefox 3 and Firefox 3.5 by Mozilla organization, July 2009
Mozilla's UAAG Evaluation Report by Mozilla organization, February 2002
Mozilla's Bugzilla bug reports: this is the publicly accessible bug reports database on all Mozilla products. Hundreds of thousands of bug reports are available via Bugzilla. All confirmed and assigned bug reports on Firefox, Seamonkey, Camino, Thunderbird, Sunbird, Minimo, etc. are available to the public.

Browser conformance test suites

HTML 4.01 conformance tests by Robin Lionheart. MSIE 7, Firefox 2, Opera 9, Safari 2 and Icab 3 are tested, measured and their results can be compared.
Several hundreds of CSS testcases by Ian "Hixie" Hickson. This has to be the most complete, thorough testsuite for modern browsers.
CSS 2.x testsuite (DRAFT) by Eric Meyer. The results of CSS 2.x testsuite page needs updating for new versions of browsers.
Current CSS 2.1 Test suite at W3C (last updated in September 2008). Firefox 3.0a9pre rv:1.9a9pre nightly build 2007092502 fails 27 tests out of 500 (5.4% failure); Opera 9.50a3 build 9542 fails 50 tests out of 500 (10.0% failure); Internet Explorer 7 fails 129 tests out of 500 (25.8% failure).
DOM 1 Core tests with JsUnit 2.0Beta TestRunner by W3C. MSIE 7 fails 85 tests out of 224 tests, a 37.9% rate failure which is well over/above the percentage rate of Firefox 2 (6.3% failure rate) and Opera 9 (5.1% failure rate).
CSS 3 Selectors test suite results by Robert Blaut
User Agent Accessibility Guidelines 1.0 Test Suite for HTML 4.01 (draft) by W3C's WAI
Web Compatibility Test for Mobile Browsers Although aimed at mobile browsers, this test is suitable for screen, visual browsers. Internet Explorer 7 and Internet Explorer 8 beta 2 fails 8 tests out of 16, a 50 % rate failure, Firefox 3.0.1 and Konqueror 4.1 fail 5 tests out of 16, a 31.3 % rate failure, Safari 3.1.2 and Safari 4 fail 4 tests out of 16, a 25 % rate failure, Firefox (Shiretoko) 3.1 (rv:1.9.1b1pre build 20080919) fails 3 tests out of 16, a 18.8 % rate failure, Opera 9.60 beta 1 fails 0 tests out of 16, a 0 % rate failure.