Accessibility Testing Tools

A few things I like to have to hand, so publishing them is the easiest way for me to have them available easily...

Extensions

High contrast (Edge), not quite the same as Windows High Contrast mode, but useful.
Landmarks & headings (Edge/FF) pops up a navigation tool, which also gives you an overview of the landmarks.
Skip to landmarks/headings (FF)
Social visual alt text (FF) - automatically shows alt-text for images on facebook/twitter/linkedin.
Stylus (Edge) / FF) - lets you create CSS sheets to change the appearance. I have a few gists, the CSS ones.
Web developer (Edge / FF), swiss army knife of dev tools, including showing alt-text, deleting cookies, outlining headings, resizing the window for reflow testing.
Arc toolkit (Edge) / FF), run in browser automated tests.
IBM Equal Access Accessibility Checker (Chrome/Edge, Firefox)
Ian Lloyd’s bookmarks (in an extension - Edge), or as bookmarklets.

Follow the link, the drag the appropriate link to your bookmarks toolbar

Landmarks, Headings, Lists, Images, Forms
Text spacing
Character key shortcuts
ARIA usage
HTML Validator (for Parsing checks) — note works in partnership with bookmarklet below but does not require installing
WCAG Parsing only (to strip non-accessibility related issues from HTML Validator results)