Two weird errors?

Question

Today I got two errors which I would like to understand better, they might be related but I'm not sure.
The first error was that the syslog-ng daemon didn't want to start at boot up. It only gave an error message along the line with "couldn't find libcap.so2". I could still start up X, but there when I tried to launch firefox it only gave me the error message "couldn't load XPCOM".
At that point I figured they where related so I rebooted into a terminal and did
pacman -S libcap
which gave me alot of "file exists in filesystem error" which I get kind of frequently. Sorry about not having the exact error messages, but basically it was alot of "/usr/share/*" stuff that already existed in the filesystem. Now I did what I normally do; a pacman -Qo [file], checking so no package owns the files and then
pacman -Sf libcap
Now this solved the first problem, syslog-ng was running again, but this did not resolve the firefox issue.
I tried to resolve this by completely removing firefox with
pacman -Rs firefox
but that resulted in
package "firefox" not found
How could this happen, firefox is installed on my system but somehow pacman has forgotten all about it?
Any way I got firefox running again by doing a
pacman -Sf firefox
Where I need to force the install since all the files are already there, and leaving out the "f" gives me alot of those "* exists in filesystem" errors I mentioned before.
Everything seems to be working now, but I still have the eerie feeliing that something is broken somewhere. I mean why did this happen all of a sudden. I did update my system yetserday I think, is that what broke all this? It is as if pacman somehow forgets about some packages it has already installed, like in this case libcap and firefox, the files are still there but doing an upgrade messes stuff up somehow. Can someone explain what's going on here?
This turned out quit lengthy, but I really would like to understand what's going on here. So any hints are appreciated.

Answer 1

That is strange, and I can't say that I have gotten anything like this is Arch before, but I have had similar problems appear in other distros.  Usually what I do is to use Catfish (or insert your file finder of choice) to locate the offending files and delete them via superuser file manager, so that the program can be installed freshly and completely.  For example, with Firefox search for the firefox files and delete them manually so that pacman -S will install freshly and completely.
It probably was caused by an update (perhaps an update that went array) but unless you have other problems materalize, I wouldn't worry about it.  It is best to update on a daily basis, because if you wait too long between updates there is greater risk of breakage.  Pacman -Syu often and hopefully you won't have anymore problems like this.