Hi centeron, the message about the size of a request header field often refers to an excessive amount of accumulated cookies.

After completing work on the site, remove the saved cookies for the site as follows. While viewing a page on the site, try either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "Clear Cookies and Site Data"
• (menu bar) Tools > Page Info > Security > "Clear Cookies and Site Data"

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try reloading the page, log back in, and try again. Does that help?

centeron said

Your browser sent a request that this server could not understand. Size of a request header field exceeds server limit.

Using the suggested solution solves the problem temporarily. Is this a work-around to a FireFox defect? Or is this a problem with the website I am trying to access? I have yet to see this problem when using Microsoft Edge, so I am guessing it is a FireFox defect. Am I correct? If not, I can contact support for the website and let them know they have a problem.

Hi kjlaw48

This shouldn't happen normally. Possible causes are extensions that deal with cookies or external (cleanup) software that corrupts the cookies, so if you have such software then exclude Firefox.

I have 2 extensions: Grammarly and LastPass. I disabled both of them and I still have the problem. With Microsoft Edge, I only have LastPass extension, but I never have the problem when using Microsoft Edge.

The only software that is run is whatever web programming that is executed by the following website:

Mayo Clinic Online Service.  

The error occurs when I left click on the Log in to Your Patient Account button on this web page.

cor-el said

Hi kjlaw48 This shouldn't happen normally. Possible causes are extensions that deal with cookies or external (cleanup) software that corrupts the cookies, so if you have such software then exclude Firefox.

Hi Cor-el,

I contacted the support for Mayo Clinic Online services and they informed me the problem is in their web programming and they have seen the problem in both FireFox and Safari (with Apple products being the biggest problem platform). They are working on a fix and expect it to be available in about a week.