hello dcddcd, middle-clicking or ctrl-clicking a link should make it open in a new tab.

This is not normal Firefox behavior.

Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• On Windows you can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac you can open Firefox 4.0+ in Safe Mode by holding the option key while starting Firefox.
• On Linux you can open Firefox 4.0+ in Safe Mode by quitting Firefox and then going to your Terminal and running: firefox -safe-mode (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

Please report back soon.

It is possible that the website code is specifying a target window and if you have opened a link to this specific window before then it is possible that further links are opened in this tab.
You can middle-click such a link or hold down Shift and left-click to open the link in a new tab.

See also:

• http://kb.mozillazine.org/browser.link.open_newwindow
• http://kb.mozillazine.org/browser.link.open_newwindow.restriction

Thanks for all the replies. Very gratifying to know there are helpful people taking an interest. I have my middle button set to 'Back' so that is not an easy option. Holding CTRL-click did indeed force a new tab to open, but is a bit of a pain. Tried Safe Mode and the behaviour continued. Completely uninstalled and re-installed Firefox and the behaviour continued. Up until now I had replicated my moves apart from visiting various (not always the same) web sites. I had been using Findamo search engine as this seemed to be on the Firefox start page and I hadn't seen it before. I am new to Firefox as Windows Internet Explorer is becoming more and more useless as XP cannot run an iteration later than V.8 Next time I did not use Findamo and went back to Google - the strange behaviour disappeared! Hoorah. Sanity returns. Thanks for your help all.

I am glad to hear that your problem has been resolved.

If you have not already, please mark this thread as solved by marking the solution.
This will help other users experiencing similar problems find help faster and more efficiently.

I hope you continue using our products and thank you for contacting Mozilla Support.

If Safe Mode disables all add ons, then if that doesn't solve the issue, why would it then be an extension? Aren't extensions add-ons? This makes little sense.... and seems more like going in circles. I've tried Safe Mode, I've troubleshooted extensions, empty the cache, constantly, as I also constantly remove as much Inactive RAM, since FF uses up 2 to 3 Gigs, as well as sometimes jumping up to 200, 300, even 500% of CPU usage, (according to Activity Monitor), which of course is wack. But I'm getting very tired of spinning wheels making me wait, unresponsive scripts, that even if I click to Stop, just keep on going, freezes, and occasionally a full-on crash.... This goes on, with every new "update" I install....

@StevenCee
Add-ons/extensions have been known to cause various issue on Firefox.

If you issue has not been solved by any of the above, please create a question thread containing the details of your issue.
This thread has been marked as solved and most volunteers will not bother with this thread because there is no longer an issue (with the user that created the thread). Creating your own thread with notify the volunteers that you need assistance.

Please post the link to your thread below.