Tab behavior changed recently

I'm on a Windows machine. In the past, when I clicked on a link in email, a new tab was opened in Firefox leaving existing tabs active. This has recently changed and now opens in the active tab. I know about CTRL/Click, but this doesn't work from within Outlook. I tried a hack in about:config, but found that everything opened in a new tab. For example when clicking on a search list within eBay, every click then opened a new tab. There seem to a lot of tab related config settings there, so I have done a reset to get FF back to its default behavior. If there a way to open links in a new tab without forcing every click (say to the same domain) in a new tab? Might this have something to do with the new container feature?