If you're a heavy user of the web, you've probably had the same experience I have: You open too many browser tabs, and everything starts slowing to a crawl.
There are lots of reasons this can happen, but one of the most common culprits is Flash, an obsolete but still widely used technology for displaying video and interactive content. A lot of advertisers use Flash, and their animated ads consume a lot of resources, slowing down your computer even when they are in the background. Even worse, if you're on a laptop, the extra activity will drain your battery.
Also, Flash is plagued by security problems.
A while back, I found a solution to this problem: an extension that tells my browser, Chrome, not to run Flash content until I click on it. As a result, I never have to look at Flash-based ads, and they don't slow down my computer. I'm at a lower risk of hackers using Flash to take over my computer. And when I do want to look at Flash content — some video sites are still Flash-based, for example — I can activate it with one click.
If you're also a Chrome user, you can get the extension I use, called Flashcontrol, from the Chrome web store. Just click the "add to Chrome" button in the upper right and then click "add" in the dialog box that pops up.
Similar options are available for other browsers, though I can't personally vouch for them. Firefox has a built-in feature that performs the same function. Safari has ClickToFlash. I haven't been able to find a similar extension for Internet Explorer, but you can configure Microsoft's web browser to ask you before running Flash content.
This advice mostly applies to desktop browsers. Apple has refused to support Flash on iPhones and iPads, and Google phased out Flash support on Android several years ago.
Flashcontrol does cause occasional glitches. There are a couple of less popular video websites that will show a spinning "loading" icon in place of the icon Flashcontrol usually displays. It took me a while to figure out I had to click on the video to make it start playing. Also, you'll occasionally see layout problems if Flash content — usually pop-up ads — obscures the content you're trying to read.
But overall, the Flashcontrol extension has greatly improved my web browsing experience. You might like it too.