Especially it should be emphasized that the DOM - the inspector in Firefox is just plugin'om, ie it is contained in every distro Firefox, but not installed by default. As disadvantages Firefox Error Console should identify what Firefox does not filter error, ie not emit those that refer to the page you are viewing right now. In concluding the Error Console of Firefox should say that today Firefox error console is one of the better tools for debugging JavScript scripts, among tools are integrated into the browser. Debug Console Console Opera browser Opera may be a surprise discovery for the developers of web sites that are experiencing it for the first time. In addition to all the features that offers developers the error console Firefox, Opera console has some nice features: a qualitative and logical description of the error, advanced snippets of JavScript code that shows what the place a scenario in which the error occurred, the ability to filter errors by type (for example: JavScript, CSS, etc.). However, it should be noted that, unlike the console Firefox, Opera console does not support JavScript - command, this feature Console Opera is somewhat unfortunate, since such a function console of Firefox is very useful. I must say that Opera from the start showed a serious approach to web development and claimed the title One of the best web developer. Summary In conclusion, it should be said that currently the vast majority of modern browsers have implemented quality tools debugging web applications and this statement applies not only Firefox and Opera, and IE8 and the choice between them is up to each individual. In principle, for the first experiments with JavScript you can use any of the above three debuggers. Especially as, with increasing complexity Your JavScript programs you sooner or later outgrow integrated into the browser debugging tools, and you always have to think about expanding the functionality of your Web browser, by setting plugin'a, which can Firebug or become like him.