The most common reasons why bookmarks disappear include improper installation of various add-ons and accidentally disabling the bookmarks toolbar from the navigation bar. Bookmarks can also disappear if they get moved to different folders automatically or if the main user account for the Web browser is not active.
Google Chrome stores bookmarks in the cloud, allowing users access to their personal bookmarks regardless of the computer they’re using. However, this functionality may cause problems if the Google Chrome instance on a new computer doesn’t synchronize with the user's personal settings, which effectively makes the bookmarks disappear. In that case, the easiest way to restore the bookmarks is to locate the bookmarks backup file in the user data folder for Google Chrome and remove the BAK extension after disabling the automatic synchronization from the settings window within the browser.
If the bookmarks toolbar was accidentally disabled in Firefox, a user can restore his bookmarks by right-clicking on an empty space in the navigation bar and selecting the Bookmarks Toolbar option from the pop-up menu. Similar to Google Chrome, Firefox associates a single set of bookmarks with a specific user profile. In case a different user account is active, personal bookmarks may seem to disappear. This can be fixed by simply logging in with the right account or using the Profile Manager to select the correct profile.