I think this problem started after installing 3.6.9 , but not positive. I only noticed it after installing 3.6.10. I get the following error. Firefox could not install the file at http://s31.freecause.com/aadvantage_toolbar.xpi because: Unexpected installation error Review the Error Console log for more details. -203 From the Error Console, this is the first failure log followed by a number of similar and parsing messages: .unbreakable { /* display:-moz-inline-box; */ } h1.Breadcrumbs { clear:both; background-color:#363E41; font-size:17px; height:0; margin-bottom: 20px; padding-bottom:23px; } #topnav { margin-left:-5px; } .srsort { width:80%; } .OfferCell { border-right: dotted 1px #A4ADB0; border-top: dotted 1px #A4ADB0; width:200px; font: 12px arial; white-space: nowrap; font-weight: bold; padding: 10px; } #SearchResultsPanel12_pnlSearchResult, #comparebymerchant, #productComparision, #tblsearchresults, .TableSorting { font-size: 9px; margin-top:5px; } .TopTableSorter { position:relative; top:-8px; } #Primary div.Advertisement a { padding-left: 0px !important; } span.TopHeadline { /*margin-left: 25%;*/ padding-left: 0px; /*width:50%;/*width: 100%;*/ text-align: center; } span.PTText { color: #7B7B7B; font-size: 9px; font-weight: bold; margin-right: 0; text-align: left; } div#WelcomeBack ul { margin-left:-40px; list-style-type: none ; float:left; text-align:left; } div#Welcome_UserNameTextBox input { width:124px; } div#Welcome_PasswordTextBox input { width:124px; } .Advertisement a { text-decoration:none; } .AllRetailersPrint{ position:relative; right:1px; } /* 8-4-09 */ /* 08-04-09 */ .RegisteredCardsGridRow{ background-color:#fcae35; color:#555555; } .RegisteredCardsGridRow td{ padding:5px 5px 5px 5px; width:320px; } .RegisteredCardsGridRowAlternating td{ padding:5px 5px 5px 5px; } tbody th{ background-color:#e5e7e3; padding:5px 5px 5px 5px; font-weight:bolder; } #CardTypeLabel{ font-weight:bolder; } #CardNumberLabel{ font-weight:bolder; } div#ProductDetailsWrapper { width:710px; } table.ProductDetailsTable { width:710px!important; } #RegisterCardDiv{ padding:5px; background-color:#e5e7e3; } #RegisterCardDiv tbody td{ padding:0px 30px 0px 5px; cellspacing:10px; } #GetPointsDiv{ width:200px; float:right; padding:20px; } #SearchWidget_GoButton{ float:right; margin: 0px 20px 0px 0px; } .ManageCardsDiv{ position:relative; bottom:30px; } #ManageCardsHeading{ position:relative; top:10px; } div.MyFavoriteMerchantsHeaderDiv{ border-bottom:1px solid white; } div#ProductDetailsWrapper{ width:710px; } table.ProductDetailsTable{ width:710px!important; } table#tblSpecialOffersArrange td.SpecialOfferSettingCell + td.SpecialOfferSettingCell + td.SpecialOfferSettingCell{ padding-left:36px; } #topsection-subheadcontent{ width:438px; } span.Welcome_RememberMeCheckBox{ position:relative; right:39px; bottom:6px; } div.LocalSearchButton{ padding-top:3px; padding-right:41px; } table.MerchantProductPointsTable div.point-value-div { padding-top:1px; } div#map_canvas{ } div.MyFavoriteMerchantsHeaderDiv{ font-size:13px; border-bottom:1px solid #fff; } #WBData tr.WBHeader td { padding-left:5px; } div#TabbedSubmit{ position:relative; float:right; } div#Welcome_UserNameTextBox input{ width:124px; } div#Welcome_PasswordTextBox input{ width:124px; } #midsection .leftcell-copy { padding-right:0px; width:433px; } #HowItWorksWrapper{ padding:10px; } div#LoginAlreadyMemberDescriptionNote{ display:inline; color:red; font-weight:900; } #midsection #passwordvalid a{ padding-left:39px; } div#LoginAlreadyMemberDescription{ margin-top:23px; } table#midsection-table td.midcell-login{ vertical-align:top; } /*REVISED LOG-IN PAGE*/ div#midsection div#LoginVerticalWrapper div#LoginControl { width:375px; } #midsection #LoginVerticalWrapper #LoginControl div#errortext{ width:370px; margin-top:5px; } div#topsection div#midsection{ text-align:left; } #midsection td.leftcell-login{ width:400px; border-right:1px solid #666; } #midsection td.leftcell-login div#leftcell-loginHeadline{ vertical-align:top; font-size:23px; padding-left:0px; } #midsection td.leftcell-login div#lefttcell-button{ vertical-align:top; font-size:23px; padding-left:0px; margin-top:20px; margin-left:30px; } #midsection td.leftcell-login div#usernamevalid{ margin-top:20px; } #midsection td.leftcell-login div#loginbutton{ margin-left:0px; margin-right:0px; vertical-align:top; float:left; } #midsection td.leftcell-login div#loginbutton a{ position:relative; bottom:10px; width:300px; } #midsection td.leftcell-login div#loginbutton input{ padding-top:5px; padding-left:32px; } #midsection td.leftcell-login div#leftcell-login-details{ margin-top:40px; } #midsection td.leftcell-login div#LoginVerticalWrapper{ margin-left:30px; } #midsection td.leftcell-login div#forgotpassword{ margin-left:52px; width:226px; } #midsection td.leftcell-login div#forgotpassword span.Welcome_RememberMeCheckBox{ float:right; margin-top:-20px; margin-left:103px; } #midsection td.rightcell-copy{ vertical-align:top; width:327px; padding-left:50px; } #midsection td.rightcell-copy div#rightcell-loginHeadline{ vertical-align:top; font-size:23px; padding-left:0px; } #midsection td.rightcell-copy div#rightcell-button{ vertical-align:top; font-size:23px; padding-left:0px; margin-top:20px; margin-left:30px; } #midsection td.rightcell-copy div#rightcell-button-description{ vertical-align:top; font-size:12px; padding-left:0px; margin-top:20px; margin-left:0px; } #midsection td.rightcell-copy div#rightcell-button img{ margin-top:30px; margin-left:50px; } div#topsection div#OopsDiv1{ font-size:14px; font-weight:500; color:#666; text-align:left; width:465px; position:relative; bottom:210px; left:85px; line-height:130%; margin-bottom:-120px; } div#topsection div#OopsDiv1 div#OopsHeadline{ font-size:24px; font-weight:900; } div#topsection div#OopsDiv1 div.OopsDivAlt2{ font-size:16px; font-weight:900; color:#000281; margin-top:10px; } div#topsection div#OopsDiv1 div.OopsDivAlt1{ margin-top:5px; } div#topsection div#midsection{ text-align:left; } #ThirdPartyPopup { width:315px; } ul#navi { width:202px; } #NavHeader { width:202px; } div#OnlineSearchResultsWrapper{ float:left; margin-bottom:20px; } div.HeroContainerAA div.tabcontent p{ top:-17px; margin-right:8px; } div.HeroContainerAA img { height:212px; margin:0 auto; } div.HeroContainerAAFlowerTabs div#flowertabs { position:relative; top:-2px; right:-1px; height:20px; width:auto; background-repeat:no-repeat; } div.HeroContainerAAFlowerTabs div#flowertabs a{ top:-4px; } .modernbricksmenu2{ border-top:0px !important; } /* div.HeroContainerAA .tabcontent img{ width:100%; } div.HeroContainerAAFlowerTabs{ margin-bottom:15px; } */ div#OnlineSearchResultsWrapper{ float:left; margin-bottom:20px; margin-top:10px; } div#BaseDescriptionLabelDivComplete { top:37%; left:36%; }

http://kb.mozillazine.org/Unable_to_install_themes_or_extensions_-_Firefox