Firefox 3.5 is a tad buggy and unstable at times... the majority of issues will become apparent running FireVortex due to the heavy javascript.
A 3.5.x release is due out to fix numerous bugs on Mozilla's end. Even a bug day on July 7th.
Firefox 3.5.1, due in mid to late July, is planned as a “quick turnaround” update that “fixes topcrashes and bugs [Mozilla] almost held ship for.” These topfixes are a cryptography issue under Windows XP, disconnected Arabic letters in edit fields as well as crashes caused by the TraceMonkey JavaScript engine. Mozilla has not yet decided whether 3.5.1 will be labeled as a major update or if that phrase will be reserved for version 3.5.2.
.: FireVortex | Read the FAQ! :.