Improved about:config Page Makes Editing Hidden Prefs Easier

Monday January 20th, 2003

As many advanced users are aware, Mozilla has lots of 'hidden' preferences that can be tweaked to alter obscure settings or improve performance. Making changes to these prefs used to involve manually editing your prefs.js or user.js file. However, now you can alter these options directly from within the browser, thanks to the fix for bug 107418.

To take advantage of this new feature, you must be running a recent Mozilla or Phoenix nightly. Enter about:config in the Location Bar and a colour-coded list of preferences will appear. Editing them should be familiar to anyone who has ever hacked the Windows Registry: each pref now has a context menu that allows you to copy its name or value to the Clipboard, modify its setting or reset it back to the factory default value. You can also add unlisted preferences by using the 'New' submenu: select 'String' if the value of the setting you want to add is textual, 'Integer' if it's a number or 'Boolean' if it's either true or false.

Most modifications will take effect immediately but some may require a restart. Note that making changes in about:config updates prefs.js and not user.js. As the user.js file takes precedence, you'll have to manually remove any lines you want to alter from user.js (or delete the file entirely) before making changes in about:config. Finally, remember that you can really screw things up if you're not careful. You have been warned.

#1 Not working?

by ksheka

Monday January 20th, 2003 2:53 PM

Using Build 2003012008 on WinXP, I'm not getting anything. :-(

Can anyone confirm - Is it me or the build?

I've had a lot of flakiness with recent builds. If someone can point me to a reasonably good WinXP build, I guess I'll nuke my profile and try it out. :-)

#2 Re: Not working?

by ksheka

Monday January 20th, 2003 2:54 PM

By nothing, I mean that I get the Preference Name / Status / Type / Value fields on top of the window, and nothing underneath it. :-(

#4 Works for me

by chrishaff

Monday January 20th, 2003 3:28 PM

I'm using the following on XP: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.3b) Gecko/20030116

I'd back up the two files we mentions and maybe removing user.js, though I did not need to do that.

#5 Works for me

by chrishaff

Monday January 20th, 2003 3:29 PM

I'm using the following on XP: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.3b) Gecko/20030116

I'd back up the two files we mentions and maybe removing user.js, though I did not need to do that.

#6 Re: Not working?

by ruudd

Monday January 20th, 2003 3:55 PM

for me the same 8-( using phoenix-cvs from 20-01-2003 20:00CET

#9 Not for me either on 2003012008 Win2k

by nicka

Monday January 20th, 2003 6:04 PM


#8 Re: Not working?

by ksheka

Monday January 20th, 2003 4:16 PM

Apparently this is bug 189835 ( )

#3 very cool new feature

by mbokil

Monday January 20th, 2003 3:17 PM

I just downloaded build 2003011922 linux today and when I type about:config and hit enter I see all my configuration settings. Apparently you can double-click on any item and its value will pop-up with a dialog box allowing you to enter new strings for settings. I just disabled tooltips on the menubar and then re-enabled them without a problem. very nice.

Even though people like to complain abou the bloat in Mozilla, once you get used to some of these power user features it is so hard to go back to IE. Mozilla is deffinately the power users browser, er, application suite.

#7 preferential alternative

by brantgurga

Monday January 20th, 2003 3:56 PM

I haven't seen this in action since it doesn't work for me in 2003012008, but you might look into Not only can you see all the preferences, they are in a cascaded tree, have descriptions, etc.

#15 Re: preferential alternative

by Gunnar

Tuesday January 21st, 2003 7:36 AM

I just installed it on Mozilla 1.0.2 and so far I am very impressed. Thanks for the link - Preferential was something I have been looking for since I became aware of prefs.js :-)


#10 Wow, it's in Phoenix .5

by ken

Monday January 20th, 2003 8:41 PM

On a whim, I tried about:config and got the screen. Sweet.

#11 Re: Wow, it's in Phoenix .5

by kryptolus

Monday January 20th, 2003 10:40 PM

about:config has been there for a long while ... editing the prefs is new

#12 Not Enough Contract for Selected Settings

by peterlairo

Tuesday January 21st, 2003 12:18 AM

The text of the settings are green (default) and blue (user changed). The background color of a selected setting is dark gray.

When a setting is selected, ther is not enough contrast between the text and the dark gray background, thus making the text VERY hard to read.

I suggest either using a light-gray backgroud or making selected text white.

#13 That's bug 189842

by durbacher

Tuesday January 21st, 2003 6:04 AM

Look into that bug, I have posted a patch yesterday that replaces the silly blue/green with standard/bold text of the standard color. Just see the screenshot in the bug.

#14 Bug 189835 (about:config doesn't work) FIXED

by durbacher

Tuesday January 21st, 2003 6:06 AM

That was a bug introduced an hour before build 2003012008 or so. It has just been fixed minutes ago, so the later ones of todays builds should work again.

#16 XUL based?

by amutch

Tuesday January 21st, 2003 3:27 PM

Does this rely on XUL for the interface?

#18 Re: XUL based?

by grayrest

Thursday January 23rd, 2003 12:54 AM

But of course. If it's chrome in Moz (i.e. not a web page) it's XUL

#17 Background colour

by Spidy

Tuesday January 21st, 2003 6:23 PM

So with all this power, how does one change the background colour of the Messenger and it's sidebar from the default white?

#19 Re: Background colour

by grayrest

Thursday January 23rd, 2003 1:10 AM

Same way you've always done UI changes: userChrome.css

Add the following to userChrome.css in your profile (change color to whatever you want)

#folderTree{background-color:green;} #threadTree{background-color:green;}

The main message display, however, is controlled by the mozilla HTML color settings in Edit>Preferences...>Apperance>Colors>Background.

I couldn't tweak the color with the DOM Inspector, which is unusual. If anyone with greater insight can comment, I'd be interested to know why using the DOM Inspector to set background-color on the HTML element (main element in an XUL browser component) doesn't work.

#20 Documenting the effects?

by dej

Tuesday February 25th, 2003 6:31 PM

This is a really helpful capability, but it is not always obvious what the preferences actually *do*. For instance, what exactly does mailnews.nav_crosses_folders do, and what are the valid integer values? Or network.protocol-handler.external.hcp ?

Is there some documentation of these? (outside of the source tree, that is?)


#21 Memory loss

by patpm

Tuesday August 15th, 2006 6:23 AM

I am using Version : Netscape 7.1 Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) and my PC is losing its mind. The amount of memory used grows steadily (as shown in the Windows Task Manager) until I have to reset my PC (XP-based, latest service packs installed.)

I am not a hacker, I am a (fairly savvy) user of Windows based PCs and I want to know how to fix this problem. Is there a procedural fix somewhere or do I have to change over to the dreaded Internet Explorer? I also use Firefox and Opera, but I see downsides in both of them too.

#22 Memory loss

by patpm

Tuesday August 15th, 2006 6:27 AM

By the way, I tried the procedure on, but there were no blank lines on my about:config.

Danke. Pat