Compatibility/UA Override & Interventions Testing

Mozilla added a new web compatibility page to Firefox as a new about page in Firefox, in order to make compatibility modifications for Internet sites and services transparent.

These modifications are divided into User Agent Overrides and Interventions:

- Interventions - are deeper modifications to make sites compatible. Firefox may modify certain code used on these sites to enforce compatibility. Each compatibility modification links to the bug on Bugzilla@Mozilla; click on the link to look up information about the underlying issue.

- User Agent Override - change the user agent of Firefox when connections to certain sites are made. 

Some sites may use the user agent of connecting browsers to block access completely, display a different design, or provide different functionality.

Viewing the list of Interventions and Overrides on Desktop and Mobile

Desktop screenshot:

Mobile screenshot:

Verifying if the website has been fixed on their end

- Load the page by pointing Firefox to about:compat. 
- Just type about:compat in the Firefox address bar to display all web compatibility modifications that are active at the time.
- Disable modifications with a click on the disable button next to them. 
- The button toggles between disable and enable, so that you may enable the compatibility modification again at a later point in time.

What you need:

- Windows machine
- MacOS machine
- Linux machine
- Mobile device running Android