Husmail's site is working fine here. There may be some internal issue. You may try these steps to fix:

• Click the menu button and choose Options.
• Select the Privacy panel.
• Set Firefox will: to Use custom settings for history.
• Click Show Cookies.... The Cookies window will appear.
• In the Search: field, type Hushmail.
• Select the cookie(s) in the list to remove and click Remove Selected.
• Click Close to close the Cookies window. Close the about:preferences page.

If the above doesn't help, could you describe the problem in more detail. For example:

• Can you load a main page and start logging in, or can you not load anything?
• Do you have your username and password saved in Firefox's Password Manager?

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.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

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

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

• Switch to the DEFAULT theme: Firefox menu button/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

You can try to open the mail page in a Private Browsing mode window. Check that Firefox isn't blocking content in case you see the tracking-protection shield icon at the left end of the location bar.