It's now been two days, and it still continues to load the https://www.mozilla.com/en-US/plugincheck/ page every time that FireFox starts. I hope someone finds out how to turn this off, as it's very annoying!

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

Viewpoint Media Player is responsible for the plugin called "MetaStream 3 Plugin r4", and I believe this plugin is triggering Firefox to open the plugincheck page. It is not enough to disable the plugin, it must be uninstalled.

For me, after uninstalling Viewpoint Media Player, the "plugincheck always opening" problem then went away.

Also see answers to the question: https://support.mozilla.com/en-US/questions/832793

Type about:config in the URL bar and hit Enter.
If you see the warning, you can confirm that you want to access that page.

Pref = plugins.update.notifyUser if it shows as True, double-click that pref to toggle it to False

If that pref was already set to False, try disabling the QuickTime Plugin and then restart Firefox, to see if that is the culprit.

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

Viewpoint Media Player is responsible for the plugin called "MetaStream 3 Plugin r4", and I believe this plugin is triggering Firefox to open the plugincheck page. It is not enough to disable the plugin, it must be uninstalled.

For me, after uninstalling Viewpoint Media Player, the "plugincheck always opening" problem then went away.

MikeClark - removing Viewpoint Media Player did the trick for me too. Thank you.

Thanks, that did the trick. Here's what I did.

1) Went into about:config and looked at the plugins.update.notifyUser listing and saw that it was already on False. I changed it to True and then back to False. Also, the URL that is below it, I deleted the URL.

2) Went into Windows Program Manager and uninstalled the Viewpoint Media Player.

3) Went back into FireFox and selected Tools and Addons and disabled the MetaStream 3 Plugin.

Restarted the PC, and now it's back to normal where it open opens one tab with the about:blank.

Get rid of Viewpoint Media Player!!!

That is a bug with blocklisting plugins that has been fixed.
You can correct this issue by forcing the file blocklist.xml to update or wait until Firefox updates the file.
That update will remove the severity="0" flags in the file that cause the problem.

See:

• /questions/832793?page=2#answer-198407
• http://forums.mozillazine.org/viewtopic.php?p=10899869#p10899869

• Bug 663722 - The blocklist output is including severity="0" where it shouldn't be