I did this for my kids. I have a 4 year old and 2 year old who uses it.
The following are the steps I took to get this to work.
Number 1, get firefox here.
Look at the right hand of the page for the "Get FireFox LOGO".
Follow the Instructions after you download the installer.
Run Firefox After You install it.
Get Speed Dial here
.
After You have installed Firefox, You can install this plugin.
By clicking on the below link, or going into firefox, and under the pull down menu, clicking "TOOLS" and selecting "ADD ons"
https://addons.mozilla.org/en-US/firefox/addon/4810
Either way will take you the Firefox page for Speed Dial, in which you Click on the button that says add to firefox. After it is installed, Use the first time setup. This will set up Speed Dial as your home page. To check You can do so by clicking on the Pull down menu "Tools", check where it says "HomePage"
Mine looks like this. 
Just follow the instructions presented after you click on first run. You can click on a number and choose to edit it that way. Choose how many blocks you want. I used a 4x4.
I also made tabs and labeled them, kids, deals, tech, etc.
You can also drag your bookmarks into a number and it will become that link. For the kids sites, I took snapshots of the website and in edit you can "attach a thumbnail" I used a free product called 'hover snap" Which is a great simple free program.
Get Hover Snap Here.
Download Here. (authors site.)
I am attaching some thumb nails of several of kids web sites That My 2 year old likes. Yours may differ. Check the attached Zip file.
Last Set the Speed Dial as your home Page if it isn't already set.