Browser add-ons are like apps for your internet browser. They can help you save money on shopping websites or block advertisements.
Unfortunately, according to recent computer security reports, not all browser add-ons have good intentions. A recent report found that many add-ons are performing malicious activities on your PCs, including:
-Tracking every single page you visit
-Sending your information to a third party company
-Selling your browsing habits and personal information to browsers
-Injecting advertisements onto webpages, which is actually legal according to Google
These problems are currently affecting millions of users around the world. There is some good news, however, and that’s that the add-ons can’t see anything that’s going on outside of Chrome or Firefox. They also cannot see stuff you put into secure forms – like passwords, usernames, addresses, postal codes, etc.

However, they can see that your internet history shows you visiting a page like facebook.com/yourfirstnamelastname
Now the add-on knows your name.
Next, they see you’re visiting sites trying to buy diet pills. The add-on might try to inject diet pill advertisements into a page you’re visiting. Instead of buying the product you think you’re buying from the page you’re visiting, you buy the heavily-marketed product your add-on wants you to buy.
That’s bad. Really bad.
All of this tracking is hidden behind something called “Anonymous usage statistics” and “EULAs”. You know those licenses you scroll through and ignore every time you install something? Yes, developers are using those stupid things – called End User License Agreements – to track your data.
One particularly bad but popular add-on is Hover Zoom, which lets you hover over something to zoom in. Hover Zoom comes with the following permissions:

That’s sleazy, Hover Zoom. Hover Zoom also uses its anonymous usage statistics to push advertisements to you.
HowToGeek.com did a thorough investigation of this behavior here. In that article, the site takes an in-depth look at the source code to see where, exactly, the damage is being done.

The danger of add-on updates

The article concludes by stating that “loads of extensions are being updated to include tracking / spying code”. These add-ons inject advertisements and other bad things into the pages you’re visiting. They also sell your information to companies.
The bad part here is that some of these add-ons start off being completely innocent. And then they update themselves to become more evil. Web-savvy people might scrutinize their add-ons when they’re first installed, but who bothers to read through an update log?

Which extensions are guilty?

A full list of tracking extensions can be found here. These extensions have been caught injecting advertisements and selling your personal information to shady companies. Notable extensions include:
For Chrome:
-Hover Zoom (which has millions of users)
-Power Zoom
-Eat my cookies
-Fabulous
-Smooth Scroll
-GetThemAllDownloader
-Neat Bookmarks
For Firefox:
-BBC News Reader (BBC did not make this add-on; it’s from a third party)
-Autocopy
If you have any of those add-ons currently installed, I urge you to uninstall them as soon as possible.

 How to remove extensions and add-ons

-In Google Chrome, click the Settings button (the three horizontal bars in the top right corner of your screen) and then click Extensions. Disable all the extensions you don’t like.
-In Firefox, click the Firefox button at the top of the window and then click Add-ons to open the Add-ons Manager tab. Disable all add-ons you don’t like.
If you follow the above steps, you’re going to make your internet browsing significantly safer and reduce your chances of viruses, identity theft, and other bad things.