The Web Developer Toolbar add-on adds various convenient tools to Firefox for development and testing purposes.
It includes accessibility checks under Tools > Validate Section 508 and Tools > Validate WAI. These link to Cynthia Says pages which stopped working in 2013, but are still present in the toolbar and can be easily replaced with functioning accessibility checks.
In Firefox, with the Web Developer Toolbar enabled:
- Go to Tools
- Select Edit Tools...
- Select Validate Section 508
- Click Delete and confirm deletion
- Select Validate WAI
- Click Delete and confirm deletion
- Click Add...
- Replace the Description value with Validate with WAVE
- Select the URL radio button
- Replace the URL value with http://wave.webaim.org/report#/
- Click OK to save the new entry
- Click OK to close the Edit Tools dialog
Now you're all done. Visit a website and try Tools > Validate with WAVE.