Let me start with the general:

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox 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, try either:

• 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?

Nothing worked except clearing the cookie. Even then, LastPass, which is instructed to 'autologon', doesn't; I have to click the [Logon] button. I'm also perplexed why the cookie causes the problem.

FYI, I zapped the cookie using CCleaner. It was in the "Cookies to keep", so moved it to "Cookies to delete", ran CCleaner. I hope this doesn't mean that every time I go onto the site and it loads a cookie that I have to delete that cookie to get FF to work. IE does not have the problem; only FF.

Usually cookies only need to be deleted if the site changes its code incompletely (and can be confused by getting both old and new cookies), or if the cookie has become corrupted and is not updating correctly. Using external software like CCleaner to reach into Firefox's cookies database and make changes could corrupt your cookies, so that might explain the source of the problem.

As for why the LastPass add-on isn't submitting the login form, I have no idea. Probably what it does is simulate the Enter key being pressed, and if I do that on the page, the form is submitted. You might try asking about that form on the LastPass forums and see whether there's something special going on there.

I have already entered a "ticket" on LastPass's support site re LP not auto-logging me in. Thanks for the quick responses.