This is the most frustrating error. It occurs because the install.rdf file inside the .xpi sets a maximum version limit (e.g., maxVersion: 10.* ).
This article details how to locate the correct version, the challenges of legacy development, and why Firebug eventually vanished from the modern web landscape. firebug download for firefox 12
A prompt will appear asking for permission to install the software. Click "Install Now." This is the most frustrating error
The Firebug GitHub remains a repository for the original source code and historical data. 3. How to Install A prompt will appear asking for permission to
Firefox 12 was released in early 2012. Because modern Firebug versions (like 2.0.x) require much newer browser engines (Firefox 30+ or 53+), you need a version of Firebug that was contemporary to that era.
Since Firebug is discontinued, the official "getfirebug.com" no longer hosts active direct downloads. You can still find legacy .xpi files (the Firefox extension format) in these archives: