If you look at the /plugincheck page you will note it will scroll and you will then see more information. You should ensure that you have the plugins enabled before you run the check. (You also need javascript enabled, but you will get a warning if you do not.)

Are you running scriptblockers that may prevent plugincheck from working ?

I have some plugins disabled but the ones I have mentioned are all enabled. I have NoScript and AdBlock extensions installed but mozilla.org is enabled and the plugin check didn't work even when these extensions are disabled :-(

Few weeks ago I tried to disable all extensions but plugin check still didn't work.

See screenshot.

With Firefox 17.0 @WinXP I have got the same problem: All plugins are listed as unknown (Flash, Adobe Acrobat, Shockwave, Java,...) The plugins are enabled, I do not have some blocker running and it used to work with an older Firefox version. When clicking at "Check to see if your plugins are up to date" in the Add-ons Manager, the resulting page is even completely blank (no header, nothing). I need to manually surf to https://www.mozilla.org/en/plugincheck/, but then no plugin is recognized. How can I fix this, please?

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

You can also try to delete the pluginreg.dat file in the Firefox Profile Folder and maybe addons.sqlite as well to reset the plugin registry databases.

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder

Thanks for the detailed guide. I cleared the cache and all cookies, delete pluginreg.dat and addons.sqlite, start Firefox in Safe Mode, but the plugins are not recognized (and https://www.mozilla.org/en/plugincheck/ still needs to be loaded manually). What could I try next, please?

The plugin seem to be detected properly as I see the correct name and description of each of them.

Open a blank tab (about:blank) and paste the code in the scratchpad window and issue Execute > Run (also works as a bookmark/bookmarklet) The plugin check code looks at the name and description fields.

javascript:(function(){var P,p=window.navigator.plugins||{},T,t=[],i;t.push((p.length).toString().bold()+(' Plugin(s)').bold());for(i=0;P=p[i];i++){T=('['+(i+1)+'] ').bold();for(var prop in P){if(typeof P[prop]!='function'&&typeof P[prop]!='object'&&prop!='length'){t.push(T+prop.bold()+': '+P[prop]);T=''}}}window.open('data:text/html,'+t.join('<br>'),'plugins').document.close()})();

You can remove all stored data from a specific domain via "Forget About This Site" in the right-click context menu of an history entry (Show All History or History sidebar) or via the about:permissions page.

Using "Forget About This Site" will remove everything like bookmarks, cookies, passwords, cache, history, and exceptions from that domain, so be cautious and if you have a password or other data from that domain that you do not want to lose then make a note of those passwords and bookmarks. You can't recover from that "forget" unless you have a backup of the affected files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.

You can try to create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Using a test profile I found the causes for the problem:

1. In prefs.js there was an evil

user_pref("general.buildID.override", "0");

2. TabKit2 Add-on is *not* compatible with FF17 (neither 0.9.9.8 nor 0.9.9.9.beta1).

Deleting the line in the prefs.js and disabling the Add-on fixed the issue. Thanks for the help! PS: My e-mail-address is no longer accepted as e-mail address, therefore I needed to create another account with another e-mail-address.