"Signing could not be verified"

This post is here mainly for the benefit of people who encounter the same problem and are looking for a fix in vain...

This post is about Ubuntu Linux and Firefox 1.5.

I decided to completely reinstall Firefox browser in my Ubuntu because it was getting rather sluggish, encumbered by many extensions I installed during the previous months. To this end, I completely removed the "firefox" package, backed up my ".mozilla/firefox" directory and then re-installed the "firefox" package. My plan was to install all the extensions I really need from scratch and use only the bookmarks.html file from the original configuration.

However, I hit a snag while installing Google Browser Sync extension. Firefox told me that "Signing could not be verified" and refused to install it. After more digging (and help from nice people), I discovered that, in Firefox preferences, under "Advanced / Security / Security Devices", I don't have the "Bulitin Root Module" item which should be there, and this is indeed the culprit. Now, this module needs the file "usr/lib/firefox/libnssckbi.so" in order to work. However, this file was not on my disk and, furthermore, was not part of "firefox" package!

After more digging, I discovered that this file belongs to package called "libnss3" which was installed on my machine. I reinstalled this package (the file magically re-appeared), added reference to this file into the "Security Devices" window and Firefox started working correctly.

I have absolutely no idea how could this file be removed. I certainly didn't do anything with /usr/lib/firefox/ files. I hope this fix helps someone who encounters this weird problem...