This list covers some of the known problems with Mozilla Firebird 0.6. Please read this before reporting any new bugs, and watch it regularly (we'll update it as new bugs are found in the release).
Mozilla Firebird utilizes large chunks of Mozilla Application Suite code. Many of the problems you may experience in Mozilla Firebird are actually problems in this Mozilla core code. If you find a problem with page content or connectivity then it is probably a Mozilla problem and should be reported to the Browser product in Bugzilla, not to the Mozilla Firebird product. Menus, and folders on the bookmark toolbar do not always collapse correctly for Mozilla Firebird users on Windows. The "Don't ask at startup" checkbox in the Profile Manager is not working. "Use this theme" checkbox in theme install doesn't function properly and you may have to switch themes by going to Tools > Options > Themes. Also, some themes will not completely switch without a restart. Form auto-complete is still an unstable feature and may lead to crashes. Disabling of form auto-completion is not working. Firebird on Mac OS X is new and still very rough around the edges. Expect platform inconsistencies.