If you regularly walk on the Internet (and most readers of Habr do this, right?), Then it will not take you long to accumulate a large list of sites that you would like to visit later. The default bookmark manager in the Firefox browser is unlikely to suit you completely. For better organization of accumulating a collection of bookmarks, synchronizing them with other computers, or simply easier access to them, many extensions have been written. So let's consider the best of them.
Foxmarks : An extension for people with multiple computers.

Do you use multiple computers or operating systems on one? If so, then the Foxmarks extension will help to automatically synchronize bookmarks between them. It also allows
access to bookmarks from the Internet . This is a very useful extension if you use public computers to access the network without being able to install anything on them. Foxmarks synchronizes your bookmarks by saving them to a remote server. With this extension, you will forget about backing up bookmarks when formatting or changing computers. Also for security lovers there is an encryption option.
Speed Dial : icons of sites on one page

This extension came from the Opera browser. It is useful if you have a list of frequently visited sites, you want to see their previews or use the hot key 'Ctrl + 1/2/3/4 ...' for quick access to them. In the settings, you can choose how many icons will be shown on one page, sort the bookmarks into groups (they will be sorted in tabs) and choose to open a bookmark in the same tab, open a new one or create a new window.

The Speed Dial has many options for customizing each preview about your preferences. You can determine how often they will be updated. The extension can also save / load settings for use on other computers.
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Delicious Bookmarks : Del.icio.us Account Integration in Firefox

This extension is not similar to the standard del.icio.us key that each user has. It gives easy access to del.icio.us bookmarks with their integration into Firefox. With it, you can quickly add existing bookmarks to del.icio.us and categorize them with tags. You can also search for bookmarks in del.icio.us from a browser.

GMarks : Google Bookmarks integration in Firefox

Do you often use Google? GMarks integrates bookmarks from Google Bookmarks directly into Firefox. GMarks makes it easy to migrate from / to Google Bookmarks. The extension can share existing bookmarks in Firefox with new ones and does not delete or erase them.
Smart Bookmarks Bar : more free space on the bookmarks bar

Is your bookmarks bar full? Smart Bookmarks Bar This extension helps to make better use of the free space on the panel, reducing the size of each bookmark. It simply shows only the icons of sites on the panel. If the site does not have an icon, you can add it using the
Favicon Picker 2 extension. By default, when you hover over a bookmark, its name is shown. You can also hide the panel when the mouse pointer is not on the not pointed, thereby saving more space.
Other extensions
The following plugins are not included in the top 5, but also worthy of mention here.
To Read Later : This extension allows you to make temporary bookmarks to sites that you want to look at later.
Bookmark Duplicate Detector : as the name says, the extension keeps track of duplicate bookmark URLs when creating new ones. Only you need to be attentive and better to backup the base.
What other extensions do you use?