javascript:void(0); in Firefox

I've been having such serious problems with Firefox, it's barely usable and am wondering if it has something to do with javascript (javascript:void(0). In the past I've always had the option under Tools to enable javascript but it's disappeared and there is no feature to enable it. I've also had that message in Chrome but Chrome is pretty functional.
The problem with Firefox is that I can't access pages to complete purchase transactions. When I'm on a page to make an online purchase or a similar activity, Firefox is dead.
Thanks for any help you can give with your brilliant brains. ellen

Which Firefox version are you using?

If your experiencing the problem in multiple browsers, then it's most likely to do with the website and not the browser.

Assuming that you are using Firefox 24.0, which you failed to mention, herewith the information from mozillaZine:

"Disabling JavaScript in Options (or Preferences) REMOVED
Due to bug 851702, the preference to disable JavaScript has been removed from the Options. If you had disabled JavaScript via the checkbox, the preference was automatically reverted to its default state of "JavaScript enabled". You can change it back through about:config by changing javascript.enabled to false. There's probably also an add-on or two or three to provide a button."

Thus, if Fx 24.0 is in use, JavaScript is most likely enabled on your computer. Time for you to do some troubleshooting, starting with the normal steps to try:

Standard diagnostic - Firefox - MozillaZine Knowledge Base

I really need your help, folks. Today I am unable to logon to any sites for financial info (bank balance, etc) I have Firefox 24. The javascript:void at lower left of screen came on and I could not access my accounts in Firefox, Chrome, Opera). I have tried troubleshooting, searches, etc. etc. I do not believe Javascript is on my machine. How can I enable it. As you know, many sites require javascript and I am unable to access them in its absence. This problem of no accounts access has actually just come about today. Thanks very much for any help, as much of the interest has been rendered useless. ellen

Yes you have JavaScript, that is not the problem.

Did you carry out the diagnostics as presented in the link I provided for you? Had you done so, you might very well have found the same type of result as shown in this thread on MozillaZine:

Error? javascript:void(0); ? mozillaZine Forums

I've just spent hours trying to perform that diagnostics re: extensions. I can access the page in ebay where the item is I want to get but neither ebay nor paypal are accepting my passwords. What kind of weird mindset is it that Mozilla would eliminate the simple "Enable javascript" feature? Do you think that possibly uninstalling and reinstalling Firefox would help? It really has rendered the internet practically useless for me, as so many sites require JS. I ask for your patience. ellen

Starting with FF23, Mozilla, in its infinite wisdom, decided to delete the JavaScript toggle because they thought that newbies might "damage their systems". IMHO that was stupid BUT THERE IS A NEW ADD-ON WHICH DOES THE JOB AND DOES IT FLAWLESSLY. It's called JS SWITCH. If you have problems, which you shouldn't they refer you to the author's page which is written in some oriental language, so for me that was useless. It didn't matter. I activated JS SWITCH. It can work in two ways and you can use one or both. In the column under "Tools" it adds a space which may or may not have a check mark (not an x) next to Enable JavaScript. I keep JavaScript disabled until I need it so my line looks like "check mark space Enable JavaScript". If I click on that it switches to "space" "Disable JavaScript". That means the JavaScript is on. When I no longer need JavaScript check "Disable JavaScript". I wanted to explain that (more complex, not really) option first. At the bottom right hand corner of your screen there is a bright red JS. That's the second toggle. When it's bright red JavaScript is on, when it's gray JavaScript is off. I recommend only using one toggle because if you use both you can get confused. This should take care of the problem unless Mozilla deletes this add-on as well. So far they haven't. Happy toggling!