Many site issues can be caused by corrupt cookies or cache. In order to try to fix these problems, the first step is to clear both cookies and the cache. Note: This will temporarily log you out of all sites you're logged in to. To clear cache and cookies do the following:

1. Go to Firefox > History > Clear recent history or (if no Firefox button is shown) go to Tools > Clear recent history.
2. Under "Time range to clear", select "Everything".
3. Now, click the arrow next to Details to toggle the Details list active.
4. From the details list, check Cache and Cookies and uncheck everything else.
5. Now click the Clear now button.

Further information can be found in the Clear your cache, history and other personal information in Firefox article.

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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.)

• You can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• 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.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

Thank you.

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry (History > Show All History or View > Sidebar > History) or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data from that domain that you do not want to lose then make a note of those passwords and bookmarks.

You can't recover from this 'forget' unless you have a backup of the affected files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.

I have cleared resent history , cache and cookies.I have uninstalled firefox and reinstalled. using norton I have cleared temp files.I have run fire fox in safe mode and disabled add-ons.forgot all about altavista.Still comes up with a blank page on search results. altavista u.s .comes up ok but if you enter a seach query like "ebay" and enter search the page comes up blank.Thank you for your help but I have tried these already. I think this may be the result of delta taking over my home page which at the time was altavista. I change my home page back but when I restarted firefox delta replaced my home page again. went looking for any file I could find from delta and deleted this fixed the home page highjacking but the u.s. altavista still didn't work.Don't know why the canadian altavista works while it appears almost the same?

Have the exact same problem. It must either be Mozilla - or Yahoo's Altavista. I suspect the former. This happened suddenly to me, BTW. Can't relate it to anything except my recent upgrade to Firefox 12.

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

In a round about way you solved my problem cor-el ! At the end of standard diagnostic there was mention of malware so I ran malwarebytes before running profile manager. malwarebytes found 21 items some in the registry. deleted these items and tried altavista us again and to my surprise it is working ok now.I thought norton 360 would catch such things but I guess it doesn't ! will keep and run a malware program from now on. thank you for your help.

Well, I downloaded WISE 'registry cleaner' from CNET, and the problem has gone away. Am now running the latest version of MalwareBytes with a full scan, just to be sure I got it. Did not do the 'profile reset/change' offered by cor el , but will keep it in mind, as well. Also, FYI, the WISE product eliminated some other annoying problems with my PC, as well. I can recommend this.