If you notice that page elements are missing from browser to browser with no obvious source, verify that AdBlock is installed and then check that the offending element does not meet the criteria of being an advertisement. Here is a list of the classes, IDs, and various other selectors that AdBlock currently looks for:
#advert1, #advert2, #advertise, #advertisement1, #advertisetop, #advertising_wrapper, #advtop, #adwrapper, #banner-ad, #bannerAd, #bannerAdWrapper, #banner_topad, #bannerad, #bigAd, #bigad, #body_ad, #bottom_ad, #centerads, #cmn_ad_tag_head, #companionAd, #content-header-ad, #contentAd, #content_ads, #content_adv, #contentad, #dart-container-728x90, #dfp_ad_Entry_728x90, #dfp_ad_Home_728x90, #divAd, #div_prerollAd_1, #download_ad, #featuread, #featured-ads, #featuredAds, #footer_ad, #footer_ads, #game-ad, #google_ads_frame, #google_ads_frame1_anchor, #google_ads_frame2, #googlead, #head-ad, #header-ads, #headerAd, #headerAdContainer, #header_ad, #homead, #ka_adRightSkyscraperWide, #leaderAd, #leaderBoardAd, #leaderboard-ad, #left_ads, #leftad, #leftads, #logoAd, #logo_ad, #mainAd, #main_ad, #mpu2, #mpu2_container, #mpu_container, #msad, #myAd, #player_ads, #pre_advertising_wrapper, #prerollAd, #promo-ad, #publicidad, #reklama, #rh-ad, #right_ads, #right_adsense, #searchAd, #search_ads, #sideAd, #side_ads, #sidebar-ads, #sidebar_ads, #skybox-ad, #sponsorAdDiv, #sponsoredlinks, #sponsors-home, #takeover_ad, #top-ad, #topAd, #topAdSpace, #topAdSpace_div, #topAdvert, #topBannerAd, #top_ad, #top_ads, #topad, #topbannerad, #videoAd, .ADBAR, .AdBody:not(body), .AdBox, .AdInfo, .AdTitle, .AdvertContainer, .HomeAds, .RelatedAds, .SponsoredContent, .ad-300x250, .ad-banner, .ad-block, .ad-border, .ad-btn, .ad-button, .ad-cell, .ad-display, .ad-enabled, .ad-holder, .ad-img, .ad-inner, .ad-item, .ad-leader, .ad-leaderboard, .ad-left, .ad-links, .ad-right, .ad-section, .ad-served, .ad-sidebar, .ad-square, .ad-stack, .ad-text, .ad-top, .ad-unit, .ad-unit-300-wrapper, .ad-vertical-container, .ad-wide, .ad-wrap, .ad-wrapper, .ad160, .ad300, .ad728, .ad90, .adBlock, .adBottomBoard, .adBox, .adContent, .adDiv, .adElement, .adFrame, .adFrameCnt, .adHead, .adHeader, .adHeaderblack, .adHeadline, .adHolder, .adHoldert, .adImg, .adItem, .adLink, .adMiddle, .adMod, .adModule, .adOverlay, .adPanel, .adResult, .adRight, .adRotator, .adSpace, .adSpot, .adText, .adTitle, .adTopHome, .adWidget, .adWrap, .ad_1, .ad_160, .ad_160x600, .ad_2, .ad_3, .ad_728x90, .ad_Right, .ad_body, .ad_container, .ad_description, .ad_global_header, .ad_head_rectangle, .ad_header, .ad_item, .ad_leaderboard, .ad_line, .ad_middle, .ad_outer, .ad_promo, .ad_slug_table, .ad_space, .ad_text, .ad_title, .ad_trick_header, .ad_wrap, .ad_wrapper, .ad_zone, .adarea, .adbanner, .adbar, .adbottom, .adbutton, .adcolumn, .adcont, .addiv, .adframe, .adheader, .adholder, .adinfo, .adlink, .adlist, .admain, .admiddle, .adright, .adrow1, .adrow2, .ads-area, .ads-col, .ads-header, .ads-holder, .ads-inline, .ads-item, .ads-section, .ads-title, .ads-top, .ads1, .adsBlock, .ads_catDiv, .ads_div, .ads_top, .ads_wrapper, .adsbottombox, .adsbox, .adsbygoogle, .adscontainer, .adshome, .adside, .adslot_blurred, .adspace, .adtile, .adtop, .adv_300, .advert-block, .advert-box, .advert-container, .advert-content, .advert-horizontal, .advert2, .advertColumn, .advertContainer, .advertLink, .advertText, .advert_container, .advert_list, .advertbox, .advertisement-1, .advertisement-swimlane, .advertiser, .advertising_block, .advertisment, .advertorial, .adverts, .adverttext, .adwords, .afs_ads, .after-post-ad, .article_ad, .banner-ads, .banner300, .bannerAd, .banner_728x90, .banner_ad, .bannerad, .block-ad, .blog-ads, .bottom-ad, .bottom-ads, .bottom-left-ad, .bottomAds, .bottom_ad_block, .box-ads, .boxad, .can_ad_slug, .category-ad, .change_AdContainer, .container_ad, .container_row_ad, .contentAd, .content_ads, .cp-adsInited, .displayAd, .featuredAdBox, .flash-advertisement, .footer-ad, .footer-ads, .footerad, .forumAd, .gallery-ad, .google-sponsored, .googleAdSense, .googleAds, .header-ad, .headerAd, .header_ad, .header_ad_center, .header_advert, .headerad, .headerads, .home-ad, .homeAd, .homead, .homepage-ad, .homepage_ads, .horizontal_ad, .image-advertisement, .imgad, .inner_ad, .innerad, .interstitial_ad_wrapper, .ipsAd, .item-container-ad, .leaderboard-ad, .leaderboard-ads, .leftAd, .leftad, .list-ad, .logo-ad, .marketing-ad, .mid_ad, .middle_AD, .module-ad, .newsAd, .oasad, .openx, .page_ad, .pfAd, .player_ad, .player_hover_ad, .pm-ad, .post-ad, .post_ad, .post_ads, .postad, .premiumAdOverlay, .premiumAdOverlayClose, .promoAd, .publicidad, .rbRectAd, .rectangle_ad, .refreshAds, .region-top-ad-position, .reklam, .reklama, .reportAdLink, .right-ad, .rightAd, .right_ad, .right_ads_column, .rightad, .rightadv, .sb_adsNv2, .searchAds, .searchad, .searchads, .showAd, .side-ad, .side-bar-ad-position1, .single-ad, .singleAd, .sky_ad, .skyscraperAd, .smallAd, .small_ad, .smallads, .sponsor-box, .sponsoredLinks, .sponsorlink, .text-ad, .textad, .textads, .top-ad, .topAds, .top_ad, .top_ad_div, .top_ad_wrap, .top_ads, .topads, .tower-ad, .type_ads_default, .wideAd, .withAds, .wp_bannerize, .yom-ad, a[href^="http://ad-emea.doubleclick.net/"], a[href^="http://ad.doubleclick.net/"], a[href^="http://adultfriendfinder.com/p/register.cgi?pid="], a[href^="http://marketgid.com"], a[href^="http://mgid.com/"], a[href^="http://pubads.g.doubleclick.net/"], a[href^="http://us.marketgid.com"], a[href^="http://www.fbooksluts.com/"], a[href^="http://www.fleshlight.com/"], a[href^="http://www.google.com/aclk?"], a[href^="http://www.liutilities.com/"], a[href^="http://www.socialsex.com/"], a[href^="http://www.yourfuckbook.com/?"], a[id^="mg_add"], div[id^="MarketGid"], div[id^="div-gpt-ad-"], iframe[src^="http://ad.yieldmanager.com/"]