Could you describe what happens in more detail? For example:

• blank page
• endless loading / timeout
• specific error message
• broken / incomplete page

More generally:

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) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Ctrl+r to check progress.

(2) Remove the site's cookies (save any pending work first). 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 > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually.

Then try reloading the page. Does that help?

If that doesn't help, could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

The Question Details > More System Details section next to your question lists four version of the Flash player plugin:

• Shockwave Flash 18.0 r0
• Shockwave Flash 21.0 r0
• Shockwave Flash 19.0 r0
• Shockwave Flash 17.0 r0

This is likely to cause confusion on sites using Flash; the older ones should be removed.

The official method is to do a full uninstall/reinstall of Flash. You can find a link to Adobe's uninstaller in this article: https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html

But... it usually works to just physically remove the older file. To discover its location, type or paste about:plugins in the address bar and press Enter. You can use Find (Ctrl+f) for npswf to skip to the entries for Flash. Each should list the full path on disk.

On 64-bit Windows, the normal location is:

C:\Windows\SysWOW64\Macromed\Flash

If you go into that folder, be careful to delete ONLY the specific file listed in about:plugins because the others may be needed by other programs.