Move plugins to another location - Firefox
From MozillaZine Knowledge Base
This article applies equally to Firefox and SeaMonkey, and even to any browser using NPAPI plugins, which means practically anything except Internet Explorer. Don't be put off by the fact that different sections were written by different authors using different browsers.
This article may be also be applied to users that use Firefox installers; it is unsure if the Mozilla Firefox uninstaller that is provided with the installer preserves your plugins directory.
When not installing Firefox from an installer, removing the Firefox installation directory and then extracting, instead of overwriting the Firefox folder, is a good idea. However, it removes your plugins in your "plugins" folder each time, unless you're careful. Fortunately, the plugins in your "plugins" folder may be moved elsewere so that they don't reside under your installation directory and so to make your manual uninstalling of Firefox easier.
Firefox searches a few locations for plugins such as Macromedia Flash and Java. One of these locations is in a "Plugins" folder a parent folder of your Mozilla profile, if one exists. This search is done even if you have no legitimate Mozilla profile. ç
To trick Firefox into searching your folder, locate where the Mozilla profile container folder should be (for example, "C:\Documents and Settings\<Windows login/user name>\Application Data\Mozilla\Profiles\"). If this folder does not already exist, create it. Now there should be a path that resembles ".../Mozilla/Profiles" (where "..." is the actual path where "/Mozilla/Profiles" exists). Create a folder in ".../Mozilla" named "Plugins" so that now there is a "C:\Documents and Settings\<Windows login/user name>\Application Data\Mozilla\Plugins\" folder.
Now locate where Firefox is currently storing your plugins. It will be under a "plugins" folder in your Firefox installation directory (for reference, the default directory for a Windows Firefox installer is "C:\Program Files\Mozilla Firefox\plugins").
Now cut all the plugins in the real Firefox plugins directory (without "npnul32.dll" file (file name may differ on Linux) -- this file might be updated between Firefox builds, so it should be removed when manually uninstalling Firefox) and paste them into the fake plugins directory.
On Linux, and presumably on Mac OS X, the plugins directory name is all in lowercase, and there is an even simpler workaround if all your plugins are in the same directory (possibly as symlinks pointing to the actual shared object). No need to cut and paste unless the ~/.mozilla directory already exists and is not empty:
and yes, the "from" goes after the "to" in that link command. (Of course, on a 32-bit machine, it will be under /usr/lib rather than /usr/lib64)