Good reason to use a user.js file when making preference changes, instead of using about:config. One small file that has only the pref changes you made. http://kb.mozillazine.org/User.js_file I am still using a user.js file that I first created in 2003 for Firefox 0.8. I just copy it into a new Profile as soon as the Profile is created. I even have favored prefs for some of the extensions that I typically use, at the end of the file. Many times the pref is there "waiting" for me to install the related extension - the reason I have those prefs at the end of the user.js file. Firefox stops reading the user.js file when it gets to a pref that isn't being used in Firefox any longer - or used yet when it comes to an extension that isn't installed.

Bold prefs in about:config can be seen in the prefs,js file, in your Profile folder - but prefs added by extensions also appear there, too. But the list is a hell of a lot shorter than about:config, and it can be printed out to view and markup with the changes / deletions you want to make.

Tip: Keep a 2nd Profile for testing "new" extensions that you want install or "test". And let that one get "buggered up" by extensions that you end up not wanting to use over the long term. Tip 2: Back up your Profile before installing a "new" extension. If you don't like an extension, slide the "back up" back into place and delete the original Profile that you installed that extension in.

Thank you the-edmeister, that solved the problem.

I have few questions.

Question 1. Since user.js is a Javascript file, I can add extension related prefs into user.js and comment them out with /* */ whenever I don't use those extensions, in order to make sure the entire user.js gets executed.Correct ? And commenting out can be done within any part of the user.js file ?

Question 2. What if one of Firefox's (not addon's) pref, located in the middle of the file, is deprecated.How could I make sure that user.js is executed entirely ?

Question 3. The prefs that I believe I might manually change from within the extension's settings should go inside pref.js instead of user.js .Correct ?

Question 4. Does the order of the pref matter ? For example in prefs.js I have this order: pref 1 pref 2 pref 3

Can I put it like this, in user.js or prefs.js ? pref 3 pref 1 pref 2

Thanks again.

You can click the Status header on the about:config page to sort by Status and thus see all user set prefs at the start of the list in one cluster.

It is best to avoid using a user.js file to set prefs as that makes it impossible to modify prefs permanently because Firefox will (re)set these prefs on every start to the value set in the user.js file and you can easily forget that you set a specific pref via the user.js file. A user.js file is suitable to initialize prefs to a known value once when you create a new profile or to reset prefs that you modify regularly during a session to your preferred state on each start in case and is useful if you have forgotten that you changed the pref. The prefs.js file stores all modified prefs including prefs with a date/time stamp value and others that Firefox maintains itself. Such prefs should never be added to the user.js file. It is usually best to makes changes to prefs on the about:config page and copy the user_pref lines from prefs.js to user.js to prevent any errors in such lines.

User.js is not a real JavaScript file despite its .js file extension, but is interpreted (parsed) just like the pref.js file and only user_pref() calls and comments (/* */ or //) are allowed. I don't think that the order matters, but Firefox will always create the prefs.js file as an ordered list. I use empty lines to group some related pref branches (e.g. browser.tabs.* prefs)

Thanks for the info.I only used prefs.js.Installed the addons one by one and added their custom prefs in prefs.js after each installation, to make sure it works as intented. All worked fine and Firefox is noticeably faster with this new profile.My only issue with the performance is Adobe Flash at this point.Few minutes earlier the plugin container crashed while on YouTube and that crashed the whole browser.That's another topic I guess.

Thanks.