How to download Firefox extensions from addons.mozilla.org without installing them?

In Firefox, right-click on the download button and select "save link as" has always worked for me.

Go to the add-on you want to install and just right click on the +Add to Firefox button and select save link as. After downloading the file just go to File>Open File and just select the extension you have downloaded work like a charm for me.

Open the addons page in a chrome browser. Then right lick on 'Add to Firefox' link and click 'Copy Link Address'. Open a new tab and Paste the same link there. Hit Enter. It will download the .xpi file.