When multi-process plugins are enabled, Firefox has the ability to dump additional information about interactions between the browser and a plugin. This is done using NSPR logging. Run Firefox in a custom environment to enable this special logging mode.
Make sure you have write permissions to wherever you wish to save the log. Your safest bet is your home directory (C:\Users\username on Windows Vista and above, C:\Documents and Settings\username on Windows XP, and ~ (home directory) on Mac OS X and Linux).
Windows
Make sure Firefox is not running. From within a command prompt:
C:\> set NSPR_LOG_MODULES=IPCPlugins:5 C:\> set NSPR_LOG_FILE=c:\plugins.log C:\> cd C:\Program Files\Mozilla Firefox C:\> firefox.exe
The log file will be saved to C:\plugins.log (or wherever NSPR_LOG_FILE is set).
Linux
Make sure Firefox is not running. From within a bash shell:
$ export NSPR_LOG_MODULES=IPCPlugins:5 $ export NSPR_LOG_FILE=~/plugins.log $ /usr/bin/firefox
The file will be saved to ~/plugins.log (or wherever NSPR_LOG_FILE is set).