Firefox 17 Released November 20th – Technical And Security Improvements

Firefox 17 is due to be released today (from Tuesday November 20th). The Change Log includes a variety of new technical and security improvements – plus the new Facebook Messenger feature. The main new features  include:

Click-to-play blocklisting – a security feature implemented to prevent vulnerable plugin versions from running without the user’s permission. Outdated plugins (e.g. old versions of Flash Player, Adobe Reader and Java) that are blocked with the click-to-play flag will not load by default – but they can be easily activated by clicking the icon.

The full list of blocked plugins is available here – of the major plugins, outdated versions of Java, Adobe Reader and Flash Player 10.2 (and earlier) are blocked by Firefox 17. Flash Player 11.0 to 11.4 will not be blocked until Firefox 18 in 6 weeks time – considering that Flash Player is one of the plugins most targeted by malware, this seems too long a delay.

An example of an outdated Java 6 plugin being blocked by click-to-play on the Java Test webpage is shown below:


The idea is that users should update the vulnerable plugin but, if they really wish to continue, clicking the icon will let the plugin run. In our example, clicking the icon will allow the Java plugin to be tested:


Facebook Messenger (Social API) – support for Facebook Messenger, this lets you use Facebook right from your Firefox browser. Updated March 2015: this feature is now obsolete but if you just want a Facebook Messenger sidebar in Firefox try this addon.

Mac OS X 10.8 – Support for Notification Center

Awesome Bar – updated with larger icons and removal of the scrollbar. I have tested the final release version and, unless there is a last minute update, it appears that this change has not made it into Firefox 17.

Mac OS X 10.5 – No longer supported

Technical (under the hood) Updates in Firefox 17

There are many technical improvements for developers e.g. to make the Web Console, Debugger and Developer Toolbar faster and easier to use and over twenty performance improvements – including fixes around the New Tab page. Finally, there are some fixes for pointer lock and page scrolling on sites with fixed headers.

HTML5 Score – The HTML5 test score increases by 20 to a total of 392 which puts Firefox in third place amongst the major browsers tested. For comparison:

Chrome 23 – 448
Opera 12.10 – 419
Firefox 17 – 392
Safari 6 – 378
IE10 – 320
IE9 – 138

Note: these scores only indicate how well browsers support the draft HTML5 standard – they don’t necessarily mean that a browser actually performs any better. However, higher scores in the tests indicate that a browser may better cope with (and display) webpages that make heavy use of HTML5 e.g. games.

New Features Present But Disabled By Default In Firefox 17

These are new features introduced in the last few Firefox releases which haven’t yet been enabled – whilst they work ok for me it is possible they could have outstanding bugs. The more adventurous user (or those wishing to get an early view of future Firefox features) may wish to enable them – they can easily be disabled again if they cause any issues.

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


There are a lot of technical changes and fixes in Firefox 17 – in particular, security and performance improvements are welcome. These also help keep Firefox up to date with the latest web standards.

As usual, this new version of Firefox will be available to users from November 20th over several days (to avoid overloading Mozilla’s servers) – don’t worry if you check for updates (via Firefox Menu \ Help \ About Firefox \ Check For Updates) and find there are none available for you yet, just try again a day or two later.