All browsers run into problems with inconsistent cached files and obsolete or stuck cookies. Thus, when you have a problem with a particular site, a good "first thing to try" is clearing your browser cache and deleting your saved cookies for the site.

(1) Bypass Firefox's Cache

Use Ctrl+Shift+r to reload the page fresh from the server.

Alternately, you also can clear Firefox's cache completely using:

orange Firefox button (or Tools menu) > Options > Advanced

On the Network mini-tab > Cached Web Content : "Clear Now"

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site:

• right-click and choose View Page Info > Security > "View Cookies"
• Alt+t (open the classic Tools menu) > Page Info > Security > "View Cookies"

In the dialog that opens, you can remove the site's cookies individually.

Then try reloading the page. Does that help?

If you have installed any new add-ons recently that relate to privacy or security, they may be blocking information the sites expect your browser to send. As a test, you could try the site in Firefox's Safe Mode. That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

If clearing cookies doesn't work then it is possible that the cookies.sqlite file that stores the cookies is corrupted.

Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookie files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

• http://kb.mozillazine.org/Cookies
• https://support.mozilla.org/kb/Deleting+cookies

I already did all the things you suggested and it made no difference. The techs at one of the problem websites already stepped me though the entire parade of things to try. I am not the only user having these problems. They said that Firefox rewrote the JIT compiler and it was causing problems.

But websites not working is just one reason I've had it with Firefox. Ever since 22.0, often when I try to shut down Firefox, it completely locks up my PC. When that happens, CTRL+ALT+DELETE sometimes will let me into the task manager and there I can see Firefox running, but when I try to end it, nothing happens. Usually at that point, I can't even shut the system down and have to use the one-finger boot to get going again.

I've also been getting frequent message that .PDF documents may not be displayed correctly and asking me if I want to open them in a different reader.

I'm just tired of fighting problems, having to reboot three or four times, and having to use IE just to do a simple thing I've done dozens of times before.

Hi JaneEyre, I'm sorry to hear about these problems, but this seems to be all new information so it's hard not to make suggestions.

Firefox's Safe Mode disables the JIT (JavaScript compiler). If that didn't help, the JIT theory probably isn't right. If it did help, you could change a preference to disable the JIT in normal mode.

I haven't read any other reports of Firefox 22 frequently locking up the PC at shutdown (but I can't read every post here). Intermittent problems are difficult to investigate, particularly when you may have many tabs open interacting with many different add-ons, and there's no crash data recorded.

Do you have Firefox set to remove private data at shutdown? Clearing a large history or large cache can lock up my system for a couple of minutes with lots of disk access.

I don't this we have enough data to give you a diagnosis at this point.

The message that PDF documents may not be displayed correctly is a pretty common admission by the built-in PDF viewer. If that's annoying, you can change to another viewer as described in this article: View PDF files using Firefox’s built-in viewer.