About this extension

Adds a color-based indicator for the HTTP version of the top‐level document of a tab in the address bar. Green indicates HTTP 3.0, cyan indicates HTTP 2.0, yellow indicates HTTP 1.1, orange indicates HTTP 1.0, and white indicates an unknown HTTP version.

The network.http.http3.enabled about:config preference must be enabled for Firefox to make HTTP 3.0 connections. Sites known to use HTTP 3.0 include Cloudflare, Facebook, Google, Google News, Google Translate, Instagram, Microsoft News, Windows Blogs, and YouTube as well as some Cloudflare-hosted sites that have apparently opted into the functionality, such as Android Police. Certain applications may block HTTP 3.0 connections in Firefox, such as Avast Free Antivirus.

Note that indicator icons will not appear on pages loaded via service workers unless the dom.serviceWorkers.enabled about:config preference is disabled. If that preference is disabled after one has already loaded such a page, one may need to bypass their browser cache by, for example, accessing the relevant page and pressing Ctrl+F5 to get the indicator icon to appear. Sites known to use service workers include Fastmail, Gmail, Mozilla Discourse, and Twitter.

Also note that a page must be loaded after the extension is enabled for indicator icons to appear.

Known Issues:

The indicator icon isn't displayed on some addons.mozilla.org pages.
The indicator icon background color is only optimized for Firefox's native dark theme and may appear excessively dark when paired with lighter themes.
The extension is only localized for English.

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Release notes for 2

New: Alt-Svc HTTP header value information is now shown in the tooltip when the header is part of an HTTP response to provide an indication as to whether a page supports HTTP/3, but isn’t using it for whatever reason.
New: If an unknown HTTP version (i.e., a version other than 3.0, 2.0, 1.1, or 1.0) is encountered, that information should now be reported in the tooltip. (Since I’ve yet to encounter such a page, this functionality isn’t tested.)
Changed: Changed the “Request” tooltip heading to “HTTP Request URL”.
Changed: Changed the “Response” tooltip heading to “HTTP Version”.
Changed: Extraneous information such as the HTTP method (e.g., GET, POST, etc.) and URL fragment identifiers are no longer displayed.
Changed: The HTTP version text now includes a slash (/) character (i.e., “HTTP/3.0”, “HTTP/2.0”, etc.) for consistency with the HTTP/3 draft specification.
Changed: Changed the name of the background script from the generic “background.js” to “HTTP Version Indicator Background Script.js” to make it easier to determine whether errors are emanating from this extension via the Browser Console window.
Fixed: Converted the SVG indicator icons to PNG icons as a workaround for an issue in Firefox 89 beta builds in which the color black is converted to white and other colors are converted to gray thereby rendering the color-based visual cues useless.
Fixed: Changed how events are handled to fix issues with an icon not being displayed for pages that load unusually fast (e.g., example.org); the wrong information being displayed for pages that are the destination of redirects (e.g., via news.google.com); and “browser.tabs.onUpdated.addListener(...) is undefined” error messages being logged to the Browser Console window.

Fixed: Scoped the extension to only execute on http:// and https:// pages.

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