At the moment, debug version of mozilla core throws assertion regardless of warning or error. For example, the refused server connection doesn't mean a software bug. In many case, a developer doesn't care such warning and just wants to continue the debugging session to the breakpoint. However, because the core software indistinguishly throws assertion, it causes a problem for developers to debug. Ideally, debugging version mozilla should distinguish non- fatal warning and fatal error and throws assertions only on the later.
probably invalid. on windows assertions give me a stream of dialogs offering abort, retry, ignore. one moves along happily, one crashes, one quits [not respective of the order in which i listed them...]. I'm pretty sure you can do something like this on other platforms... iirc my xlib builds just print assertion and continue ... i'd have to set some env var to make them fatal. if there's a specific warning which you feel should _never_ be fatal, please file a specific bug against a specific assignee for a specific url (cvsblame prefered) indicating the line, complete w/ some justification.
Simple answer, don't build the debug version of Mozilla. That version is meant for Mozilla developers for whom the assertions actually mean something. If you need debug symbols then either pass -g to --enable-optimize or set it in CFLAGS & CXXFLAGS. Alternatively, you can debug only specific modules by using the --enable-debug-modules option so then you don't have to troll through everyone else's assertions.