Since you are unable to install the extension you should try the following:
* If you are upgrading the extension, uninstall the original version before upgrading.
* Make sure you are allowing software installation in your browser options.
How to enable software installation
* Save the extension to your local machine (by right-clicking the download link and choosing 'Save Link As...') and drag the saved file into your browser window to perform a local install.
* Install the extension in a new profile