Plug-in/Extension won't delete, crashes Firefox

Question

Forgive me for this long post. Let me know if this is better suited to a Mac help forum. I have Firefox 16.0.2 and Mac OSX 10.5.8.
Recently Firefox kept crashing every time I went to open it. I opened it in safe mode and played around with different combinations of enable/disabling plug-ins and extensions until it would open fine. The culprit was this Nielsen NetSight thing. I vaguely remember possibly downloading something from Nielsen maybe two or three years ago, but nothing recently, and I've never used anything. However, if memory serves me right, this add-on has always been floating around disabled in my Firefox settings.
There is an extension showing in Firefox called "Nielsen NetSight (Firefox Tracker Add-on) 1.0." There were also some plug-ins showing in Firefox before called "Nielsen NetSight (Firefox Tracker Add-on) 1.0" and "Nielsen NetSight (Chrome Tracker Add-on) 1.0" or something very similar to that. I disabled them all, and then Firefox opened fine.
But then things got weird-
The next morning I wake up and turn on my computer and the same thing is happening. I investigate, and it's these Nielsen plug-ins again. Could have sworn I disabled them. So I disable them again, everything works again, all is good. But then I close my laptop, open it up again, same thing - they're re-enabled.
There is no option to remove them (rather than just disabling them) in Firefox itself, so I do some Googling and end up in name/Library/Application Support/Internet Plug-Ins, and there are these files called "FirefoxTrackerPlugin.bundle" and "ChromeTrackerPlugin.bundle." I recognize the names from the plug-in names I was seeing in Firefox, and I delete the files, and then empty the trash. Firefox opens fine, and the plug-ins are no longer showing up on the plug-in list. However, the extension "Nielsen NetSight (Firefox Tracker Add-on) 1.0" is still appearing - but it is listed as disabled, and Firefox opens fine.
But then the next time I close my computer and open it back up, Firefox is crashing again. I go back into that folder name/Library/Application Support/Internet Plug-Ins and to my surprise, "FirefoxTrackerPlugin.bundle" and "ChromeTrackerPlugin.bundle" are back even though I deleted them. Now the plug-ins don't show in Firefox, but the extension shows and is listed as enabled.
So basically, I'm stuck at this point where every time my computer goes to sleep or gets turned off, this "Nielsen NetSight (Firefox Tracker Add-on) 1.0" Firefox extension re-enables itself and these two files "FirefoxTrackerPlugin.bundle" and "ChromeTrackerPlugin.bundle" reappear in the plug-ins folder. This has been happening repetitively over the past few days.
In the periods right after I delete the plug-in files and remove them from the trash, I have searched my whole computer for things with names like "Nielsen" or "FirefoxTracker," etc, but I'm not seeing anything. The only thing that showed up was in my Firefox profile folder, in the extensions folder some file called prefs.js with a bunch of code. It appeared to correspond to about:config extensions.installCache. In that, there's a bunch of stuff and
....[{"name":"app-system-local","addons":{"[email protected]":{"descriptor":"/Library/Application Support/Mozilla/Extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/[email protected]","mtime":1382126687000},"{23fcfd51-4958-4f00-80a3-ae97e717ed8b}":{"descriptor":"/Library/Application Support/Mozilla/Extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/{23fcfd51-4958-4f00-80a3-ae97e717ed8b}","mtime":1332977526000}}},{......
Interesting thing about this is the rest of the code is referencing a different folder than /Library/Application Support/Mozilla/Extensions/. All the rest of it looks at /Users/myname/Library/Application Support/Firefox/Profiles/eiey9ybc.default-1381002852316/extensions/, which is where my extensions are. There was a single folder in /Library/Application Support/Mozilla/Extensions/ with nothing in it. So I deleted it. (Probably shouldn't have, since I have no idea what I'm doing, but whatever). Then I tried deleting any /Library/Application Support/Mozilla/ altogether, since everything seems to be saved in the Firefox folder, not the Mozilla folder anyway. Unsurprisingly, that didn't work, and this plug-in keeps reappearing and the extension keeps re-enabling and every time it is enabled it crashes Firefox.
Anyway, anybody have any idea how I can delete this thing so I don't have to keep opening Firefox in safe mode?
Something similar happened a few months ago, but I couldn't figure out what was going on and ended up restoring factory settings. I'd rather not do that since 1) it doesn't seem to have worked last time, 2) I don't feel like reinstalling all my add-ons and fixing all my settings, and 3) I can get Firefox to work perfectly fine so long as my computer never goes to sleep - it definitely seems to have something to do with these Nielsen tracker plug-in things, since Firefox works fine whenever they are disabled.
Not really expecting responses, but thank you in advance to anyway who might know anything.

Answer 1

That wasn't the answer, but I appreciate the help. Nothing related is in the login items (just iTunes and a thing for my phone).
Further discoveries though:
When I was in system preferences, I saw Other- Plugsuit, and went in there. Under "unmanaged," "NielsenWebKitTiger" is there. If I click the little gear underneath and click "show in finder," I end up at Macintosh HD/Library/Application Support/SIMBL/Plugins/NielsenWebKitTiger.bundle/. I tried to delete this, but it keeps reappearing like the others when I restart the computer.
Furthermore, I have now found the extension's location-
Macintosh HD/Library/Application Support/Mozilla/Extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/[email protected]
Tried deleting this, also keeps reappearing.
It is particularly confusing to me that I have so many different extensions folders. What is the difference between
Macintosh HD/Library/Application Support/Mozilla/Extensions/
Macintosh HD/Users/My Name/Library/Application Support/Mozilla/Extensions/
and
Macintosh HD/Users/My Name/Library/Application Support/Firefox/Profiles/eiey9ybc.default-1381002852316/Extensions/
The rest of my extensions are in the last of those three.
(And also, what's even the difference between Macintosh HD/Library/Application Support/ and Macintosh HD/Users/My Name/Library/Application Support/?)