If you installed the extension, but are no longer able to see the blue icon, try the following: first verify that it is active. To see all of the active and inactive extensions in your browser, check your extensions settings page. For Google Chrome, you can get there by typing chrome://extensions/ into the address bar and pressing the Enter key (about:addons for Firefox).
If the icon does not appear next to your address bar, click the Extensions button (looks like a puzzle piece) in the top right-hand corner, and make sure that it is pinned to the toolbar.
For Google Chrome
Verify that the extension is active. To see all of the active and inactive extensions in Google Chrome, check your extensions settings page. You can get there by typing chrome://extensions/ into the address bar and pressing the Enter key.
Verify that the extension is active. To see all of the active and inactive extensions in Firefox, check your addon settings page. You can get there by typing about:addons into the address bar and pressing the Enter key.
https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars