Turn off JavaScript in Firefox
With Firefox, you can get Add-ons that control/block JavaScript. (On my system, one gets Add-ons by selecting "Add-ons" on the "Tool" menu. This brings up a dialog to control Add-ons, which includes the ability to find Add-ons.) I'm currently using NoScript, which appears to be quite popular. What is good about NoScript is that it blocks everything by default, and you can allow it to allow JavaScript to run on selected sites. You can give temporary or permanent permission. In my setup, an icon appears in the lower right part of the window, and a right click in the web page proper includes a NoScript menu option.
There are other Add-ons that appear to do the same thing, as a search of the Firefox Add-on options showed. NoScript was a name I recognized, and it has worked well enough that I don't really feel the need to try anything else.
You can shut JavaScript off completely with no Add-on by going to the Preferences. On my system, Preferences is on the Edit menu. (Windows, I think, might put it on Tools.) On my system, "Enable JavaScript" is found after selecting the "Content" tab of the preferences dialog. The problem with this approach is that it will kill JavaScript completely, and one might need or want JavaScript for some sites. Of course there is always the option of having two web browsers--one with JavaScript, the other without. Normal people would hate this, but historically I've always had 2 browsers in active service--a primary browser, and a secondary one to handle the things the primary one doesn't do or do acceptably, and I don't find it to be a real problem juggling two browsers.
Link is to Noscript page:
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noscript.net