If you’re a Firefox web browser user, you already know that thousands of free Firefox add-ons exist.  There are pages and pages of add-ons to try.  While some of them are pretty ordinary and really not necessary, some of them can be really useful.  I’ve tried dozens so far and I’ve come across 10 of them that I simply can’t live without now.

Below is my list of must have Firefox browser add-ons.  If you have some add-ons you would like to recommend, leave them in the comments below so I can check them out.

Undo Closed Tabs Button – This add-on is by far my very most favorite.  I can’t count how many times I have accidentally closed an open tab only to lose everything I’ve spent hours working on.  Well, this little bugger has saved my butt a time or two since I downloaded it.  If you close a tab by accident, you just click the icon and poof the tab is reopened at exactly the same spot you left it.  Genius!

Cool Previews – If you ever find yourself just wanting to peek at a link before you actually click into the site  itself, then Cool Previews is for you.  When you hover your mouse over a link, a preview icon will pop up.  Mouseover the icon and the page comes up in a convenient preview window.  This add-on is great for double checking your own links to make sure they are operating properly.  Quick and easy.

Read It Later – With so many blogs around, you’re bound to find some interesting articles you would like to save for future reading.  I don’t know about you but links seem to get lost within my bookmarks list never to be looked at again.  With Read It Later, you can add links into a smaller reading list and save your bookmarks for your favorite sites.  The icon is put into your browser bar and you can easily read the articles, then delete them.  I use this one daily now.

Wisestamp – Configure your own custom email signature complete with social profiles in a snap.  You can set up and store personal and business signatures and have them automatically inserted whenever you draft an email.  Super easy to setup and very professional looking.  Bonus: add your rss feed address and it will insert a link to your most recent article too!

Search Status – Curious to see how other websites or blogs rank in comparison to yours?  This add-on displays the Google PageRank and Alexa rank right within your browser.  View them instantly with no fuss involved.

ReminderFox – Keep important dates and to do lists straight in one manageable application.  You can set up the reminders to go off daily, weekly and even yearly.  Choose when and how often you want to be reminded of tasks and special occassions.  A reminder box will appear and you can choose to snooze it for a bit or mark it complete.  I have birthday and bill reminders set up so I don’t miss my important dates.

SEO Blogger – This convenient add-on lets you search for keywords directly from your blog editing page.  A seperate sidebar opens up on the same page so you can write and optimize your posts at the same time.

IE Tab – If you have a website or blog then you know that your site can appear different to readers using Internet Explorer than it does in Firefox.  This super cool add-on can let you see how your site appears in IE without you actually having to open it in IE.  One click opens up an IE tab within Firefox.

MeasureIt – Instantly get the pixel width and height of any webpage element by drawing out this handy ruler.  It may be hard to get a 100% accurate measurment but it’s an excellent tool for something that doesn’t need to be an exact measurement.

TwitterBar – I was very skeptical about this one at first but it really is cool!  You simply type your Twitter message in your browser address bar along with –post and poof, off it goes to Twitter!  I couldn’t believe how fast it is.  A really nice tool if you don’t feel like opening any other Twitter app or Twitter itself.