You can just visit the plugin check page and update your plugins. This would prevent it from opening next time.

That just started happening like 24 or so hours ago, based upon 10 other forum threads. One user has helped us narrow it down to a few plugins that become disabled with a hidden preference, and he said that problem was gone with that pref disabled. "We" need to figure which Plugin is causing that.

See if disabling the QuickTime plugin makes that not happen. Or maybe the Flash plugin?

Tools > Addons - Plugins - disable one Plugin and then restart Firefox to see if that solves it

BTW, you do have at least 2 Plugins that should be updated - Java and Flash

Did that -- no change. Still adds the plug-in check tab/page.

I uninstalled Viewpoint Media Player (and the AOL IM client AIM, since apparently that's what forced Viewpoint Media Player on to my system.)

For me, the plugincheck problem then went away.

I don't know why I installed AIM -- I know better than to do that! In the past I've used the open source IM client "Pidgin" to talk to people on AOL IM and it worked fine. And it doesn't have any advertisements, toolbars, or shady "media players" like AIM does. I'll go back to using Pidgin now! Bye AIM!

Fixed ! Updated apple Quicktime from 7.1 to 7.69 and the problem stopped. Had to download the new version, go to administrator login, uninstall v7.1, install new version. This eliminated the extra plugincheck tab in the admin account immediately (next start of FX). In user account, had to open it once (with plugincheck still present) to let FX see that the plugin had been updated, then close FX and restart.

What didn't work: disabling ALL plugins and extensions; updating Adobe Flash Player; updating Java 5 u6 to Java 6 u26; screaming and yelling; asking all my friends.

BTW, 'm still running Adobe Player 9.4.4, but will upd to 10.0.1, anyway.

Based on mikeclark's experience with another plugin, IMHO, this is a Firefox-created problem that exists in v3.6.17, at a minimum. That is, unless Quicktime and Viewpoint Media Player use the same code (which is not out of the realm of possibility). Why it showed up June 10, 2011 is a mystery as .17 and QT have been installed for longer than that. (Is FX modifying code in the plugincheck without asking permission through an update ??)

@jtru

I'm not sure why that Plugin Check page just started appearing on June 10th, but but I think it is connected to this preference plugins.update.notifyUser becoming set to True. How that happens I don't know - but it is connected to this Bug report about a new feature that was added to Firefox 3.6 when it was being developed in 2009 - https://bugzilla.mozilla.org/show_bug.cgi?id=514327

Based upon mikeclark's postings13 to 15 hours ago, I started to get a handle on what might have happened. Now after getting a good night's rest, I was planning on re-tracing my steps to see if my thought process missed something that is key to figuring this out, but that ain't gonna happen because it seems the mikclark edited all the postings he made about his problem.

It's the QuickTime Plug In. It has a red ! in the add on list. Update it and the problem went away. Some sort of emergency security update.

This problem is caused by an incorrect update to the blocklist.xml file.
https://bugzilla.mozilla.org/show_bug.cgi?id=663722
(Please don't comment in that Bug report, posted for viewing only.)

More information here. - https://bugzilla.mozilla.org/show_bug.cgi?id=663676

You'll get a new blocklist.xml file automatically within 24 hours of this problem being fixed on the server. Firefox automatically looks for a new version of that file every 86400 seconds.