CustomizeGoogle is a Firefox add-on that lets you customize various Google products/services such as Google Web Search, Gmail, Google Calendar, Google Reader, etc.
Pictures speak better than words, let's look at the configuration screen of Google Web Search:
The descriptions of the options in the dialog box are pretty descriptive already so I'll only talk about the ones I like.
First of all, if you check Add links to other web search sites, you will see a list of links to other search engines on your search result page:
If you check Use Google Suggest (suggest words while you're typing), you'll see a dynamic drop down menu when you enter your search phrase in the Google search box:
This is actually a feature of Google Suggest and you should have seen it if you played around in Google Labs before.
This one is a handy one, Give the search box focus. Most of the times after you perform a search, you'll want to refine the search by adding more keywords. Without this checked, you'll need to click the search box with your mouse before you can alter the search phrase.
If for some reason you would like to see the position counters of the search results like Yahoo does, you can check Add position counter and the search results will look like this:
I like this one the most, Stream search result pages [BETA]. With this checked, you'll see more and more search results as you scroll down the search result page. In some sense it's like a "infinite search well". The nice thing about this is that you never have to click "Next" or "Previous", just scroll up and down!
For Google Image Search, there's a nice option called Rewrite links to point straight to the images:
This is one feature that I think Google should have done long time ago. Very often when I do an image search, I'm only interested in the images, not the websites that contain them. In the past, I always have to click two times before I can see the original images. With this you can see the image directly by clicking the Original Image link:
Don't know why Google can't think of this with all the smart people (O__O )
It also has options for other Google products such as making Gmail secure (using https). I'll let the readers explore the rest of them :)