Firefox 15 debugger to go into beta next week

Among the enhancements queued up by Mozilla in the next weeks for the new Firefox beta will be a new debugger for web applications. Firefox's JavaScript engine has been providing debugger support to extensions, most notably Firebug, for some years, but with Firefox 15, the entire debugging interface of Spidermonkey, the JavaScript engine, has been redesigned. This has eliminated much of the performance penalty that comes with running JavaScript code with a live debugger and it allows the debugger to be run remotely. The latter feature means that developers will be able to debug applications running on Firefox for Android or Firefox OS from a desktop or laptop computer.

Other new features of the debugger include the fact that when opened it will list all the page's scripts in a menu but complement that with a search box; this allows rapid navigation using partial filenames and ":" to go to line and "#" to go to search term. The debugger can also be triggered by the keyword debugger in the JavaScript source code, making it appear when that line is executed, or it can be called up on exceptions. It can, of course, also be called up with a Control-Shift-S or Cmd-Opt-S keyboard shortcut. A simple toolbar will offer the debugger's controls (resume, step over, step in and step out) while stack frames and in-scope variables are shown in a panel on the right.