I'm not sure if you mean tabs or tags (you say tabs in the subject, then you say tags in the message). If you get a drop-down menu when clicking on the blue web feed icon, that means there is more than one feed available.

From there, just select the feed you want to view. See Live bookmarks

Thanks Chris but that doesn't solve the problem. I meant "tabs" by the way. The drop down menu doesn't work. Instead, when I click on the icon, multiple tabs start opening.

Extensions can sometimes be the cause of problems. If the problem does not occur in Safe Mode, then you can disable your extensions one-by-one until you find out which one is causing the problem. See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Make sure that you haven't selected Firefox as the application for RSS feeds. See Firefox repeatedly opens empty tabs or windows after you click on a link

Check the Web Feed settings: Tools > Options > Applications > Web Feed (Preview in Firefox) You can also check the pref browser.feeds.handler (Filter: feed*handler) on the about:config page and reset them to ask.

To open the about:config page, type about:config in the location (address) bar and press the Enter key, just like you type the url of a website to open a website. If you see a warning then you can confirm that you want to access that page.

No use. I think this is a Firefox bug because it worked in previous versions. The only way I can make it work is by setting a different application as the RSS reader (eg Safari) - but this is really clumsy. Unless Firefox fixes this, I think I'll kiss it good-bye.

Your Firefox settings and info are kept in a folder separate from the Firefox program, called your profile folder. Try creating a test profile, to see if the problem still occurs. See Profile Manager - Create, remove or switch Firefox profiles

I have exactly the same problem on three different macs but RSS feeds works just fine with safari on the same machines

I have exactly the same problem on 3 macs. RSS feeds with Safari work great.