During all this chapter, we introduced you to Chrome DevTools. It's one of the most powerful tools for debugging JavaScript applications, but it is important to see the reality of the web market. Just look on this graphic below from StatCounter GlobalStats, http://gs.statcounter.com, that provide statistics from more than 3 million websites.

As you see, there exists more than one web browser, and Internet Explorer with Firefox together represents a bit less than 50 percent of the market. It means that your web mapping application must be compliant to those other browsers. Moreover, you have to deal with different versions for the same browser family.
Although OpenLayers itself works really well with all browsers, your own code will not always do it.
Because of this, we'll review some tools to debug in Internet Explorer and Mozilla Firefox. We will describe equivalence between Chrome DevTools panels and browsers-specific debuggers.
Before Internet Explorer 8, there wasn't any debugger built-in. The previous version of OpenLayers library (the 2.x series) was covering old IE versions such as IE 6, 7. OpenLayers 3 supports IE 9+.
Although the IE debugger is considered less powerful than other browsers debuggers, it is valuable tool in particular because of the step-by-step debug.
The following screenshot of IE 9 debugger shows that most panels are similar to Chrome Developer Tools:

The HTML panel is like the Elements panel, and the CSS and Scripts panels do the same job that the Sources panel in Chrome DevTools does.
The Console and Network panels are quite similar to the ones in Chrome Developer Tools.
In addition, for better performance, for example, to evaluate and improve your JavaScript execution time, a profiler can be found in the Profiles panel but doesn't provide as much functions as its Chrome equivalent.
With IE, each version of the browser debugger gains panels. So, it would be better to review versions differences using the official Microsoft developer website at http://msdn.microsoft.com/en-us/library/ie/.
Like for IE, this part will be dedicated to describe equivalence between Chrome DevTools and Firebug, an extension to Firefox. Although Mozilla Firefox has a built-in debugger included nowadays, Firebug remains the best tool on Mozilla to debug web maps and sites at the time of this writing.
We advise that you install it by visiting the official site at https://getfirebug.com/.

Now, it's time to make the comparison again.
In this case, the Console panel with the DOM panel in Firebug provides the same functionality that Chrome Developer Tools Console panel gives.
The HTML panel is equivalent to the Elements panel.
The CSS and Script panels combined together give you Sources panel functions.
The Timeline, Profiles, and Audits panels are specific to Chrome Developer Tools.
Most of the extensions for Firebug are listed at https://getfirebug.com/wiki/index.php/Firebug_Extensions.
Those extensions help to close the gap between default Chrome Developer and Firefox with only FireBug.
You can also find Mozilla Firefox add-on that do not always depend on FireBug. The official place to get them is https://addons.mozilla.org.
If you need one extension, you will have to install Acebug: https://addons.mozilla.org/en-us/firefox/addon/acebug/.
When you are learning and in particular doing JavaSript test directly in the browser, it behaves like an advanced text editor. Its main goal is to bring new features to Firebug's multi-lines command.
This add-on does the following:
Moreover, the Resources panel that you get with AceBug in Firebug combined with Cookies panel provides similar experience to the Resources panel in Chrome DevTools.
More and more efforts have been done on the built-in Firefox Developers Tools, it starts widening the gap with Firebug debugging functions. Sometimes, it exposes more advanced capabilities than Firebug. You can take a look at it main dedicated page at https://developer.mozilla.org/en-US/docs/Tools.
Learning process goes through repetitions. So, go back to the previous Console panel examples of the chapter and retry them in Mozilla Firefox. Take your time to see differences with Chrome Developer Tools behaviors. After those tests, go to your first OpenLayers example and type ol in the Console panel and click on it to browse like if you were in the Chrome Developer Tools Console tab. We also recommend that you play with autocompletion. Don't hesitate to experiment until you feel confident.
Q1. What panel(s) will you use if you wanted to execute JavaScript code?
Q2. You want to make some changes in CSS styles; what panel(s) can be used?
Q3. Using the sample from Chapter 1, Getting Started with OpenLayers, when you inspect the map object with console.log, what methods are available?
map.getView().map.getLayers().map.getLayer().map.getInteraction().