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Add-ons won't download or install

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I've tried to install from the Mozilla add-ons site and directly from the publisher's web site. From Mozilla I keep getting a message the add-on didn't download and I should check my connection. Directly from the publisher Firefox claims the file is corrupted. What gives? Since Firefox killed AdBlock Plus I wanted to install either Ghostery or AdBlockerPlus and both crapped out.

I've tried to install from the Mozilla add-ons site and directly from the publisher's web site. From Mozilla I keep getting a message the add-on didn't download and I should check my connection. Directly from the publisher Firefox claims the file is corrupted. What gives? Since Firefox killed AdBlock Plus I wanted to install either Ghostery or AdBlockerPlus and both crapped out.

Chosen solution

The add-ons are not dead, and the connection problem most like is not you, it's Firefox. A critical certificate used in verifying add-on signatures expired, so you need a hotfix to install, enable, or update most add-ons. More info in this article:

Add-ons disabled or fail to install on Firefox

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Chosen Solution

The add-ons are not dead, and the connection problem most like is not you, it's Firefox. A critical certificate used in verifying add-on signatures expired, so you need a hotfix to install, enable, or update most add-ons. More info in this article:

Add-ons disabled or fail to install on Firefox