How do you extract symbols from official binary builds of Arch? According to official documentation (https://wiki.archlinux.org/title/Debug_-_Getting_Traces and bug report threads I've seen), Arch lacks both debug packages and symbols bundled with binary packages. As a result, if you want to debug an app crash on Arch, you need to quit the program, recompile the app from source with your makepkg.conf set to !strip, then try to reproduce the bug in your new build.
Only public symbols and unwinding information is extracted from Arch packages because they don't have debuginfo like other distros. It's better than nothing.
Well that's unfortunate to hear :( Hoping Arch can fix releasing debug symbols for official binary builds soon... but I don't expect it to happen soon.
Also how does unwinding info help during debugging? Does gdb use it? Do I need special reverse-engineering tools to extract useful information?
Arch already uploads symbols for their Firefox builds so that's OK, it's the dependencies that are missing. Unwinding information is used to produce accurate stacks. If it's lacking our unwinder has to rely on heuristics to discover the frames on the stack and those might end up producing suboptimal traces.
It seems Firefox has a script at https://github.com/gabrielesvelto/symbol-scrapers/blob/maste..., but I haven't investigated what it does. In any case, this information should be integrated into the Arch Wiki.