Improve accessibility tooling documentation

Add links to useful browser extensions and learning resources to the
FE-accessibility documentation.

doc/development/fe_guide/accessibility.md

@@ -5,8 +5,16 @@
 [Chrome Accessibility Developer Tools][chrome-accessibility-developer-tools]
 are useful for testing for potential accessibility problems in GitLab.
 
-Accessibility best-practices and more in-depth information is available on
-[the Audit Rules page][audit-rules] for the Chrome Accessibility Developer Tools.
+The [axe][axe-website] browser extension (available for [Firefox][axe-firefox-extension] and [Chrome][axe-chrome-extension]) is
+also a handy tool for running audits and getting feedback on markup, CSS and even potentially problematic color usages.
+
+Accessibility best-practices and more in-depth information are available on
+[the Audit Rules page][audit-rules] for the Chrome Accessibility Developer Tools. The "[awesome a11y][awesome-a11y]" list is also a
+useful compilation of accessibility-related material.
 
 [chrome-accessibility-developer-tools]: https://github.com/GoogleChrome/accessibility-developer-tools
 [audit-rules]: https://github.com/GoogleChrome/accessibility-developer-tools/wiki/Audit-Rules
+[axe-website]: https://www.deque.com/axe/
+[axe-firefox-extension]: https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/
+[axe-chrome-extension]: https://chrome.google.com/webstore/detail/axe/lhdoppojpmngadmnindnejefpokejbdd
+[awesome-a11y]: https://github.com/brunopulis/awesome-a11y