Do a malware check with a few malware scan programs. You need to use all programs because each detects different malware.

http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware http://www.superantispyware.com/ - SuperAntispyware http://www.safer-networking.org/en/index.html - Spybot Search & Destroy http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page .......... See also "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

Go to Help->Troubleshooting information.

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Then more will be known about Firefox settings and extensions on your computer so supporters will be more able to help you.

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Troubleshooting Information
  This page contains technical information that might be useful when you're
  trying to solve a problem. If you are looking for answers to common questions
  about Firefox, check out our support web site.
 Application Basics
  Name   Firefox
  Version 5.0
  User Agent  Mozilla/5.0 (Windows NT 5.1; rv:5.0) Gecko/20100101 Firefox/5.0
  Profile Directory
  Enabled Plugins about:plugins
  Build Configuration about:buildconfig
  Extensions
  Name   Version  Enabled ID
 myBabylon EnglishBB Community Toolbar3.5.0.12true{b2e293ee-fd7e-4c71-a714-5f4750d8d7b7}
 Conduit Engine3.3.3.2falseengine@conduit.com
 Download Accelerator Plus (DAP) extension9.5.0.0false{F17C1572-C9EC-4e5c-A542-D05CBB5C5A08}
 Microsoft .NET Framework Assistant1.2.1false{20a82645-c095-46ed-80e3-08825760534b}

 Modified Preferences
  Name  Value
accessibility.typeaheadfind.flashBar0browser.history_expire_days.mirror180browser.places.importBookmarksHTMLfalsebrowser.places.importDefaultsfalsebrowser.places.leftPaneFolderId-1browser.places.migratePostDataAnnotationsfalsebrowser.places.smartBookmarksVersion2browser.places.updateRecentTagsUrifalsebrowser.startup.homepagehttp://search.speedbit.combrowser.startup.homepage_override.buildID20110615151330browser.startup.homepage_override.mstonerv:5.0browser.startup.homepage_override_urlhttp://search.speedbit.comextensions.lastAppVersion5.0general.useragent.extra.microsoftdotnet( .NET CLR 3.5.30729)keyword.URLhttp://search.speedbit.com/searchresults.asp?src=default&q=network.cookie.prefsMigratedtrueplaces.database.lastMaintenance1309347897places.history.expiration.transient_current_max_pages10726places.last_vacuum1300666470print.print_printerHP Officejet Pro L7500 Seriesprint.printer_HP_Officejet_Pro_L7500_Series.print_bgcolorfalseprint.printer_HP_Officejet_Pro_L7500_Series.print_bgimagesfalseprint.printer_HP_Officejet_Pro_L7500_Series.print_commandprint.printer_HP_Officejet_Pro_L7500_Series.print_downloadfontsfalseprint.printer_HP_Officejet_Pro_L7500_Series.print_edge_bottom0print.printer_HP_Officejet_Pro_L7500_Series.print_edge_left0print.printer_HP_Officejet_Pro_L7500_Series.print_edge_right0print.printer_HP_Officejet_Pro_L7500_Series.print_edge_top0print.printer_HP_Officejet_Pro_L7500_Series.print_evenpagestrueprint.printer_HP_Officejet_Pro_L7500_Series.print_footercenterprint.printer_HP_Officejet_Pro_L7500_Series.print_footerleft&PTprint.printer_HP_Officejet_Pro_L7500_Series.print_footerright&Dprint.printer_HP_Officejet_Pro_L7500_Series.print_headercenterprint.printer_HP_Officejet_Pro_L7500_Series.print_headerleft&Tprint.printer_HP_Officejet_Pro_L7500_Series.print_headerright&Uprint.printer_HP_Officejet_Pro_L7500_Series.print_in_colortrueprint.printer_HP_Officejet_Pro_L7500_Series.print_margin_bottom0.5print.printer_HP_Officejet_Pro_L7500_Series.print_margin_left0.5print.printer_HP_Officejet_Pro_L7500_Series.print_margin_right0.5print.printer_HP_Officejet_Pro_L7500_Series.print_margin_top0.5print.printer_HP_Officejet_Pro_L7500_Series.print_oddpagestrueprint.printer_HP_Officejet_Pro_L7500_Series.print_orientation0print.printer_HP_Officejet_Pro_L7500_Series.print_pagedelay500print.printer_HP_Officejet_Pro_L7500_Series.print_paper_data9print.printer_HP_Officejet_Pro_L7500_Series.print_paper_height 11.00print.printer_HP_Officejet_Pro_L7500_Series.print_paper_size_type0print.printer_HP_Officejet_Pro_L7500_Series.print_paper_size_unit1print.printer_HP_Officejet_Pro_L7500_Series.print_paper_width  8.50print.printer_HP_Officejet_Pro_L7500_Series.print_reversedfalseprint.printer_HP_Officejet_Pro_L7500_Series.print_scaling  0.90print.printer_HP_Officejet_Pro_L7500_Series.print_shrink_to_fitfalseprint.printer_HP_Officejet_Pro_L7500_Series.print_to_filefalseprint.printer_HP_Officejet_Pro_L7500_Series.print_unwriteable_margin_bottom0print.printer_HP_Officejet_Pro_L7500_Series.print_unwriteable_margin_left0print.printer_HP_Officejet_Pro_L7500_Series.print_unwriteable_margin_right0print.printer_HP_Officejet_Pro_L7500_Series.print_unwriteable_margin_top0privacy.sanitize.migrateFx3Prefstruesecurity.warn_viewing_mixedfalse

Graphics

Adapter DescriptionRADEON 9200 SE Family (Microsoft Corporation)
Vendor ID1002Device ID5964Adapter RAMUnknown
Adapter Driversati2dvag
Driver Version6.14.10.6462
Driver Date3-23-2004
Direct2D EnabledBlocked on your graphics driver. Try updating your graphics driver to version 10.6 or newer.
DirectWrite Enabledfalse (0.0.0.0, font cache n/a)
WebGL Renderer(WebGL unavailable)GPU Accelerated Windows0/1

You may want to reset the pref keyword.URL on the about:config page:

http://search.speedbit.com/searchresults.asp?src=default&q=

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.
You can use the Filter bar at to top of the about:config page to locate a pref more easily.