You can use another extension called FEBE (https://addons.mozilla.org/en-US/firefox/addon/2109) which is for backing up and reloading of all the plugins - really handy when renewing the system
Firefox can be forced to reload plugin by removing files xpti.dat and compreg.dat from profile directory of profile wherein this plugin is installed.
For example if my profiles are stored in C:\Documents and Settings\your_account\Application Data\Mozilla\Firefox\Profiles
and I want to reload plugins in profile dev
, then I will find here a profile direcotory with name like k3gh5xtb.dev
. In this directory you can find files mentioned above (xpti.dat
, compreg.dat
). These files you have to delete. That's all.