Download HTML Validator

Name: HTML Validator
Author: Morgan Jackson

By: Morgan Jackson Add-on

Download HTML Validator (current and past versions) for Firefox

Latest Version: 3.5.5 Updated: a month ago

Ready to install?

HTML Validator is available to install from Firefox Add-ons Store and for download from this page.

View source code

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Total downloads

Available versions

You can find the current and older versions of HTML Validator here. You can download the archived versions or inspect their source codes.

As a free user, you can download up to 3 latest versions.

Unlock older versions with Pro

Version	Download	Size	Download count	Timestamp
3.5.5	XPI · ZIP · Source code	13.56KB	0	2026-09-21

2026-09-21 · 0 downloads

XPI ZIP Source code

Install XPI file

An XPI file, short for "XPInstall," is a compressed file format used primarily by Mozilla applications, like Firefox and Thunderbird, to distribute and install add-ons or extensions. These files are similar in function to CRX files for Chrome but cater to the Mozilla ecosystem.

Simply drag-and-drop the XPI into Firefox to install the add-on.

Install ZIP file

Download the HTML Validator ZIP file.
In Firefox browser, go to about:addons to open Add-ons Manager
Click on ⚙, Install Add-on From File
Select the HTML Validator ZIP file from step 1. HTML Validator is now installed on your browser.