Let's see what Firefox is sending. If you open the Web Console (Ctrl+Shift+k) and then load the page, you can click the top URL in the console and a little page of headers will pop up. These will include the User Agent that Firefox is sending to the server. Does it look like this:

Mozilla/5.0 (Windows NT 5.1; rv:25.0) Gecko/20100101 Firefox/25.0

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Yes, for user agent the console shows

"Mozilla/5.0 (Windows NT 5.1; rv:25.0) Gecko/20100101 Firefox/25.0"

See also:

• http://browserspy.dk/useragent.php

Maybe you could tell the site a little lie about what browser you're using.

This extension enables you to do that on a site-by-site basis: ua-site-switch.

When you install it, it adds a yellow hard hat icon to the Add-ons bar. If you don't normally display the Add-ons bar, you can show it temporarily by pressing Ctrl+/ (which also is the keyboard shortcut to close it).

While viewing the site where you want to log in, click the hat and a dialog will come up where you can paste the user agent string you want Firefox to send that site. There's no OK button, you just press Enter after the text.

You could try the string for Firefox 24 and see whether that will work:

Mozilla/5.0 (Windows NT 5.1; rv:24.0) Gecko/20100101 Firefox/24.0

Screen shot attached (from a site in a different thread...).

Tried the ua-site-switch add on with the FF 24 string but it didn't work. Still can't get the Wordpress log in page to load.

Did trying the site in Safe Mode make any difference? If it also fails in Safe Mode, that would rule out a Firefox extension as a possible culprit.

Do you have any add-ons or external software that may be blocking or modifying your user agent? You confirmed in the console that Firefox is setting the agent string appropriately when sending the request, but there is a possibility that is being changed after it is sent.

It's also possible that the diagnosis you got from HostGator might be wrong. There might be something else about the request that is causing it to be considered suspicious. For example:

• Do you have any add-ons or external software that filters any information sent to servers such as the referring site information (HTTP_REFERER) or cookies?

• Do you use any add-ons or external software that might alter the IP address of your connection, such as a private VPN, anonymizing, or TOR service?

Trying in safe mode made no difference. I don't have any add-ons or external software blocking or modifying the user agent as far as I know.

It is possible that HostGator support was wrong as his suggestion was to just use a different browser because modifying the security mod rule was not worth the loss of security (?). I have no anonymizing or other stuff like that.

I am on a reseller account at HG hosting my own personal sites and those of my clients but I can't get the Wordpress admin page with FF. This just started happening in the past few days.

I've been using this reseller account for Wordpress sites for about three years with no problems until now. Guess I'll just use Chrome for the Wordpress sites until something changes or a working solution is found. I do appreciate all of your suggestions and ideas. Thanks.

Oh, one other thing: My ISP is a satelllite Internet service provider. Don't know if the latency may have any effect but I was able to use Wordpress in FF up until the past few days and I've been using this satellite connection for over 5 years.

In reading about "Not Acceptable" problems in a web search, this occasionally can be caused by a plugin, but one would expect that to be more consistent between browsers.

Someone also mentioned the encoding of accented characters as a potential problem. If you have accented characters in your username or password, or elsewhere in your form submission there could be a problem with the way Firefox is encoding (or not encoding) the form variables.

Obviously you know your username and password. To see what else Firefox will submit, view the source code of the page (Ctrl+u) and scroll down to the <form> section. I've got two hidden inputs:

• redirect_to
• testcookie

Do you see anything in the values for those or other inputs that might not be A-Z, a-z, 0-9 and therefore require encoding?

mod_security may also monitor IP addresses. If you route your Firefox connection differently than your other browsers, for example by using a custom proxy setting in Firefox, perhaps that explains the difference between browsers? You could check that here:

orange Firefox button (or Tools menu) > Options > Advanced > Network mini-tab > "Settings" button

The default is "Use system proxy settings" which should use IE's settings, or you could set "No proxy".

I'm not using any accented characters in my username or password. I also am not using any forms. I am trying to get the Wordpress admin page which fails to load when I point the FF browser to http://website.com/wp-login.php . Instead of the Wordpress login page I get the Mod-Security error page you see in the attached screen shot.

I checked the settings as you suggested and the default "Use system proxy settings" was present and selected. I tried with "no proxy" and still got the same error message. Meanwhile I have been using Chrome for Wordpress work and am surprised to find it is even slower than FF.

Hi kelley2100, if you can't even load the wp-login page, that quite different than what I was thinking about, which was getting an error when submitting the login form.

Do you have HTTPS configured for login and/or administration? If so, can you check the certificate information by clicking the padlock icon and see whether it shows any unexpected information about the issuer of the certificate? Some security software may intercept secure connections and I'm wondering whether that might be a factor.

I don't think I have HTTPS configured. I did try to load the page using HTTPS and had to confirm an insecure certificate (I'm using a Hostgator reseller account so the client's domain does not use a nameserve with his domain but a generic HG "websitewelcome.com" domain.

HG has been bought up by some giant corporation (EIG) that is buying many hosting company and I have read, heard and experienced degraded tech support since. I had to wait 12 hours for the first response for help on this issue and as you can see, I am still forced to use some other browser than FF to access the Wordpress accounts. So I am looking for a new webhosting company after many years with HG and I am using Chrome for Wordpress stuff.

I very much appreciate all your help with this but I think it may be a lost cause due to HG so I will just use Chrome. Thanks for trying.

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data from that domain that you do not want to lose then make a note of those passwords and bookmarks.

You can't recover from this 'forget' unless you have a backup of the involved files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I was getting ready to try your "forget about this site" idea and loaded the failing wp admin page to create a history entry when surprise, surprise, the admin page loaded into the browser and I logged in. This makes me think that this was a HostGator problem the entire time.