Firefox 21 Released – What’s New

Firefox 21 has been released today with enhanced privacy, performance and many other technical improvements as reviewed below:

Check On Firefox Start Up Times – Firefox will now suggest how to improve its own startup time if it is too slow. A popup message offers a link to learn how to speed it up (it directs you to the following help page). The default check is whether the average of your last 5 startups is more than 60 seconds. Personally I think this is an incredibly slow time to check for – I wouldn’t be happy if it was regularly taking more than 20 seconds…

You can change these default values to a more aggressive level by opening Firefox and typing about:config in the address bar then press Enter. Click the “I’ll be careful I Promise” warning button to reveal a long list of browser preferences.

Type browser.slow into the search box – this should filter the Preferences to just the following three:

  • browser.slowStartup.maxSamples – default is 5. This is the number of startups to derive an average time from – 5 should be fine for most users.
  • browser.slowStartup.notificationDisabled – default is false i.e. the startup time check is enabled. If you want to disable startup speed checking completely, double click this Preference to change its value to True. I turned it off as my Health Report (discussed lower down) confirmed my average startup is less than 1.2 seconds, mainly thanks to a fast SSD boot drive :-)
  • browser.slowStartup.timeThreshold – this is the warning threshold in milliseconds. Changing this to 20000 (i.e. 20 seconds) or less would provide a more realistic warning for most users. See our tips to speed up a slow computer.

Do Not Track (DNT) Enhancement – DNT used to offer only 2 options: Tell sites you don’t want to be tracked or Don’t tell sites anything about your tracking preferences. FF21 adds a third option – Tell sites that you want to be tracked.

You should only choose this new option if you specifically want websites to track you so that adverts are targeted i.e. more relevant to you – at the expense of a certain amount of privacy… To configure DNT, open Firefox Menu / Options (or Tools / Options if the Menu Bar is displayed), click on the Privacy tab and choose which of the three tracking options you prefer:

DNT tracking options

Health Report (preliminary) – This is an early version of the full Firefox Health Report (FHR) – it sends data to Mozilla on things like: operating system, PC/Mac, browser version, the number and type of add-ons. You can read more detail about FHR at Mozilla’s blog here.

Your individual Health Report can be viewed by browsing to about:healthreport from the address bar or by selecting Help \ Firefox Health Report from the menu/menu bar. Mine is shown as an example below:

Firefox health report

Crucially (from a privacy perspective) FHR does not collect IP addresses or track website visits, downloads, or search details – in fact, any information which could directly identify you as a user. Mozilla also promise to delete individual browser data after 180 days.

It is designed to provide information to Mozilla so that they can make Firefox better – and to help users resolve issues. It is therefore recommended that FHR is left turned on (it is enabled by default). However, if you really want to opt out of FHR, open Firefox Menu / Options (or Tools / Options if the Menu Bar is displayed), click on the Advanced tab then the Data Choices tab and untick ‘Enable Firefox Health Report’:

Firefox Health Report option

New API for Social Network Providers – Cliqz, Mixi (for Japan) and msnNOW (nope, me neither!) have been added, in addition to Facebook Messenger (introduced in FF17) which lets you use Facebook right from your browser. To use these social providers, see Mozilla’s blog page here and check that the value of social.enabled in about:config is set to ‘true’.

Other Changes – these include the ability to Restore removed thumbnails on the New Tab Page, Graphics related performance improvements, Changes to aid developers, HTML5 improvements, Stability fixes and Security fixes – see the official Release Notes for more details.

New Features Present But Still Disabled – These are new features introduced in the last few releases which haven’t yet been enabled. Whilst they work fine for me it is possible they could have outstanding bugs but more adventurous users (or those wishing to get an early view of future features) can choose to enable them – they can easily be disabled again if they cause any issues:

1. Click to Play – this feature (configure all plugins to only load on click) is still not enabled by default. However, you can activate it via a change in about:config – see Activating Click To Play and Add a Button to switch Click To Play on or off.

2. In Content Preferences – this feature (Firefox Options open in a new tab instead of a separate window) is also still not enabled by default. However, you can activate it via a change in about:config – see Enable In Content Preferences.


FF21 includes several new features plus many fixes and changes to enhance privacy and performance. As usual, this new version is available as an upgrade for existing users from today over several days (to avoid overloading Mozilla’s servers).

If you check for updates (via Firefox Menu \ Help \ About Firefox \ Check For Updates) and find there are none available yet, try again a day or two later. It is already available for full download at Mozilla here.