If extensions do not have an install button then they are installed by other software in a location that isn't controlled by Firefox.
You need to uninstall them from with the preferences of that application.

See also:

• https://developer.mozilla.org/en/Installing_extensions

• http://kb.mozillazine.org/Uninstalling_add-ons
• http://kb.mozillazine.org/Uninstalling_toolbars

Why are you talking about install buttons? It is not the lack of an install button that is the problem - it is the lack of a Remove button.

The affected addons do not have a Preferences button, so I cannot uninstall that way. That's the whole problem - in disabling them Firefox has also removed all the buttons that would allow me to simply remove the addons.

I have already read the article on uninstalling addons - that's why I now have Add-on Compatibility Reporter.

The business that owns the addons (DivX) does not offer support to non-customers and does not currently have a forum.

So I need a workaround. Please.

Cannot Uninstall an Add-on

• https://support.mozilla.com/en-US/kb/Cannot%20uninstall%20an%20add-on

Check and tell if its working.

I have read that article - the Uninstall button is not greyed out - it is missing.

There are ZERO buttons beside these addons.

No, the addon is not working - that is why it is disabled.

> Now they have no "Remove" button, even in safe mode, so I can't get rid of them.

• I have read the help articles.
• I have restarted in safe mode.
• I have searched my computer for Firefox files.
• I have searched the creator's website (they no longer support one of the addons).

Please suggest something I have not tried yet.

-> Create a New Profile as a test to check if your current profile is causing the problems.

-> Basic Troubleshooting: Make a New Profile

• https://support.mozilla.com/en-US/kb/Basic%20Troubleshooting#w_8-make-a-new-profile

-> If that New Profile works then you can recover your Bookmarks and Passwords from the Old Profile.

-> Recovering important data from an old profile

• https://support.mozilla.com/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile

Check and tell if its working.

I created a new profile, unaltered, and the DivX addons are already in the list. So, it is nothing to do with the profile.

DivX also appears in the Plugins list, along with QuickTime, Shockwave, etc. Perhaps those are OK, as divx is a file format.

It is the Addons I need to get rid of.

I posted the link to installing extensions so you can see that other software has a way to install extensions via other ways.
Extensions installed that way do not have an uninstall butto because they are not managed by the Firefox extension manager.

A possibility to prevent extensions from installing that are not installed by you is to create a new Integer pref with the name extensions.enabledScopes and set the value to 1.

• https://developer.mozilla.org/en/Installing_extensions#Disabling_install_locations
• http://mxr.mozilla.org/mozilla-central/source/toolkit/mozapps/extensions/AddonManager.jsm#1238

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold(user set).
• Preferences can be reset to the default or changed via the right-click context menu.

I did install them myself. At the time there was some software that said it needed DivX to play properly, so I installed the addons. The software still didn't work, but I did not remove them straight away, and a couple of days later, Firefox upgraded, and locked them in.

>> I have searched the creator's website (they no longer support the addons).

Avoiding future problems is all very well; I still need to fix this problem.

Uninstalling Manually

• https://support.mozilla.com/en-US/kb/Cannot%20uninstall%20an%20add-on#w_uninstalling-manually

Check and tell if its working.

Finally tracked down the extensions - I had already looked in as many places I could think of - in my own library, and in the system library, both in Applications Support and any folder named Firefox or Mozilla.

Anyhow, there they were at last, in system:Library/Application Support/Mozilla/Extensions

Don't know how I missed that in the first pass, but removing those did the trick.

All sorted :)

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Thanks for the link to these instructions.

Evidently however, perhaps there is a non-compliant or unhandled aspect of the DivX Player add-on. I followed these instructions carefully, and found that the curly-braced folders that were supposed to contain the DivX extensions were already gone. (I had previously tried the uninstaller which came with my original DivX installation.)

Searches for text within files or in filenames found nothing on my OSX 10.6.8 system, except a ChronoSync log which had previously backed up these files before they were uninstalled.

A curious scenario has developed:

My system is crashing seriously since a Firefox 12.0 update a few days ago. Since the DivX add-ons have been out of date for a long time; since it was possible the missing extensions might be causing problems; and because the disabled DivX add-ons had no remove buttons, I next tried re-installing DivX.

As soon as the re-install process completed, it detected that the previous version was out of date.

I allowed the latest update to be downloaded and installed, and, with the new version of DivX, the old add-ons were missing (there is now 1 in the place of 2), and the up-to-date versions can be re-enabled at least.

As I've just completed this, I have no idea as yet whether this is going to fix anything. But it is curious to discover at this point that with the previous add-ons disabled, they were not updating.

I'm not sure whether I'm going to try and uninstall them manually, now that an enabled version at least exists (likewise without a remove button), but I might just give that a go, and see if they disappear from Firefox finally.

It would be nice if there were a way to delete the disabled add-ons from the internals of Firefox.