The extensibility of Mozilla Firefox is one of the main reasons fans of the browser love it so much. Firefox has the same kind of evangelical adoration that Mac lovers heap upon Apple devices. It's with good reason.

Firefox is fully featured, solid, standards compliant and cross-platform. With the lighter Google Chrome still a work in progress and Apple's Safari failing to convince Windows users, Firefox remains the only credible challenge to Microsoft's Internet Explorer hegemony.

In Greasemonkey, Firefox finds a kindred spirit. Much of the Firefox interface is made for customisation, from the browser's outer skin to its many add-on extensions. Greasemonkey takes this principle further, enabling you to change the content and layout of pages you're browsing safely and securely.

To install Greasemonkey follow the instructions and then check out these best of breed Greasemonkey scripts for your surfing pleasure.

1. Greased Lightbox

Lightbox is an AJAX package that displays a full-sized image in a floating, centred layer in your browser when a thumbnail is clicked.

The page is visible below, but greyed out. Greased Lightbox takes that functionality and stuffs it into Firefox, so that any linked image you click on pops up in a Lightbox window.

2. Google scripts

Google's apps are partly driven by JavaScript, so they're prime targets for interface tweaking with Greasemonkey – many of which fix perceived oversights in Google's own designs.

Folders4Gmail adds a feature to Google Mail that lots of people find lacking. All it really does is add sub-labels to labels, enabling you to build nested categories – but it feels like you have folders!

Google Docs: Download is another add-on feature that makes you wonder why it's not already there. You can export documents from Google Docs in selected formats – but the option's buried away in a menu. This script creates a button on the toolbar.

Download

3. Facebook features

For some, the fact that Facebook exists is annoying enough. Spare a thought for its users – assaulted by virtual Mafiosi, quiz requests and zombies. Facebook Purity puts a stop to all of that, blocking messages from all third-party applications.

If Facebook adverts bug you too, you can get rid of them with the descriptively named Remove All Facebook Ads. The script blocks ad code using a DOM interception method, and although it hasn't been updated for a few months, it was still working at the time of writing.

4. Twitter tweaks

Take-it-or-leave-it social media sensation Twitter has several search tools. Google has yet to join that merry band so far, but don't let that stop you. Greasemonkey script Twitter Search adds the five most recent tweets matching your keywords to Google's search results.

There are tools that add features to Twitter's site too. Our favourite is Nested Twitter Replies. If it came in a tin, that's what would be written on it.

Nested twitter