Without doing anything wrong, your browser sends out information that makes you unique on the internet. This basically betrays your efforts to stay anonymous (unless you know what you are doing).
Every time you visit a website, your browser sends (or makes available) information about your browser configuration to the site. This information includes content such as fonts, browser type, elements supported, etc. In many cases, this will allow a site, network or bad actor to track you across the internet without cookies.
Open another browser tab and visit Panopticlick from the EFF. It will perform browser fingerprinting and tell you how unique you are in a sea of web citizens.
So what can you do to stay anonymous?
Every prepper knows that the best defense is blending in. Blending into the crowd means you are less likely to be targeted. When you travel, don’t look like a tourist waiting to be pickpocketed with a giant dSLR hanging from your neck.
The same holds true in the digital world. When a security professional wants to blend in, he/she will make his computer look as normal as possible. Using common browsers, minimal plug-ins, etc. IF you want anonymity, don’t be a digital survivalist: running noscript, UBlcok Origin, turning off Java, etc.
Modern browsers were designed for convenience and not for privacy.