en-gb dictionary (couldnt find URL, but alun has linked
)ABP https://addons.mozilla.org/en-US/firefox/addon/1865
allows you to block elements such as pictures/flash content, primarily for advert control
auto-pager https://addons.mozilla.org/en-US/firefox/addon/4925
when browsing a site that has a list over several pages, this plugin pre-fetches the following pages, and rendersd them directly below the curent one, allowing you to seamlessly scroll through long lists. works well on forums, or multi-page hardware reviews
check4change https://addons.mozilla.org/en-US/firefox/addon/3028
automatically refreshes a page, and alerts you if there have been any changes since the previous refresh
download statusbar https://addons.mozilla.org/en-US/firefox/addon/26
displays downloads in a handy bar at the bottom of your screen, allowing you to quickly check the status of multiple downloads without having toi pen a new window
glasser https://addons.mozilla.org/en-US/firefox/addon/7336 (make sure to use use 1.0.16 as newer version are not compatible with FF 3..0.0.10)
merges the navbar into Vista's Aero, allowing FF to mimic IE8 and change colour with Windows
and the vista-aero theme https://addons.mozilla.org/en-US/firefox/addon/4988
IMO the best IE8 clone skin available
