I probably have a wrong setting, but when I open my g-mail account in Safari and do the download, it goes right to my download

Can you help me?

I have several g-mails with PDF attachments. I am unable to download and save them. I get an error message with a g-mail url, along with a message unable to download. I probably have a wrong setting, but when I open my g-mail account in Safari and do the download, it goes right to my download folder. I have 1 active add-on, WOT, and I am on a new laptop. Site Advisor (McAfee) is disabled in Add-ons -no longer supported, and I don't know how to uninstall it. Mac Yosemite 10.10.3 and Firefox 37.0.2 Can you help me?