How do I resolve Javascript syntax errors suddenly popping up on most web sites I visit?

In this excerpt from
Answercast #95 I look at some odd javascript errors, possible causes and
solutions.

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Javascript syntax errors

Well, yes and no. I can only guess where that is coming from because it’s unlikely that all of these different sites are actually using JavaScript – and all have a JavaScript error, an actual error, in what they’ve encoded on their web pages.

What’s more likely is that there’s something on your machine that is causing that.

Possible virus

Now there are two scenarios that come to mind. One is you have malware on your machine – or perhaps more correctly, you have an attempt at malware on your machine – that has left some kind of trace of malware in a way that is impacting your browser.

Maybe it’s trying to hijack your browser, and is failing, or doing something else that has somehow caused a problem with your browser.

Browser add-on failure

Now, it could be an add-on. I would certainly start by disabling all of the add-ons.

More likely, though, is that this is malware. It’s a bad install of that malware. Yes, malware is not perfect. It can in fact fail and fail in some very interesting and confusing ways.

Anti-virus scans

The very first thing I would do is to run a complete and fully up to date anti-malware scan – both anti-virus and anti-spyware if you have two separate tools

I would probably also grab a copy of the free tool from malwarebytes.org and run a complete scan with that as well.

Corrupt browser

The other thing that comes to mind is that something in the browser itself is corrupt. It broke for reasons unknown.

What I would do in that case (if the malware scan doesn’t resolve the issue for you) is I would reinstall the browser. I would uninstall the browser completely first and then reinstall that browser.

Alternately you could switch to a different browser.

Software conflicts

While I was thinking this through a third option came to mind. That is that the anti-malware tools themselves could be impacting the browser.

Many anti-malware tools will attempt to scan any pages you’re viewing as you’re viewing them; as they get downloaded. That can interfere, at times, with the browser’s access of those files; access of what’s in those pages.

It’s a complex timing interaction. It doesn’t happen for everyone and it doesn’t happen all the time.

The thing to look for there is to go to your anti-malware tools and make sure that anything that might be considered “real time scanning” of browser pages, of your internet browsing, is actually turned off.

You can temporarily turn off your anti-malware tools completely – but only do that temporarily just to see if the problem goes away. Turn them back when you’re done.

What you’re really looking for is an option that controls whether or not your anti-malware tools are looking at your web browser’s pages as they are being downloaded. That can sometimes interfere with the browser in such a way that weird things like this can happen.

(Transcript lightly edited for readability.)