If you've installed the Firefox extension but you can't see the icon, it most likely just needs to be 'pinned' to the toolbar. Please follow the steps below:
1. In Firefox, locate the extensions jigsaw piece icon to the right of your address bar and click it - you should see the Sciwheel extension listed:
2. Right-click (Command or CTRL click) the Sciwheel extension listing, and select Pin to Toolbar
You should then see the Sciwheel browser extension icon to the right of the address bar.