I like to share my personal add-ons for Firefox. These add-ons have been evolved from many usages previously and belong to my favourite list. Note that maybe not all of them are usable or interesting to you, but you can always to try for a while before throw it out again at your liking. I only list which might be useful for you. Let's start!

• Adblock Plus, for filtering the ads. This one very useful in Multiply and it's not against their TOS. I recommend this one if you didn't have it before.
• CuteMenus - Crystal SVG, for adding cute icons in the Firefox menus. Of course you can live without it, but it will be a dull menus. Give it a try, and I am sure you'll never want to miss this add-on anymore.
• FlagFox, just if you curious about the location of a website, this add-on can show you exactly which country. It will sits on the bottom right corner and display the flag of the country of the currently displayed website.
• FoxClocks, perhaps you talk with friends from several countries around the world and you wonder what time is there. Don't guess, just install this one and you will be presented with information of several location around the globe. Nicely sits on the default bottom left corner on Firefox window, this can be changed freely.
• Google Icon, now it is a very pleasing to my eye when I got results from Google search with small icons on the left of every single link. This might not everybody's favourite, but I just like it that way. Alternatively, you can use GoogleEnhancer.
  
• CustomizeGoogle, for more custom option of Google related site like search, mail, news, etc. This one particularly useful for me because it can reveal the true URL of the image in Google Image Search. No more hassle with intermediate page, like before or other image search engines.
• Download Statusbar, as I like to see the progress of my downloads but hate to keep it in another window. This add-on can put downloads information in the status bar, and only with a glance I know what really happened there.
  

There are several more add-ons that I had installed, but they serve my personal taste and might not interest you at all.

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