To clear temporary files on Firefox under Windows or Mac, click Tools->Clear Recent History (or press the Shift, Ctrl, and Delete keys all at once on Windows) and it will bring up the following screen:
Make sure the Time Range is set to ‘Everything’ and Browsing & Download History, Cookies, Cache, Active Logins and Site Preferences are checked. Then click “Clear Now”. Restart Firefox and try the website you were having trouble with again to see if the problem is resolved.
Some pages, such as Webcampus.unr.edu, require pop-ups to be enabled. To enable pop-ups for a specific site, click Tools->Options and then click Content among the icons along the top so it looks like the following screenshot:
Click the Exceptions button and then enter in the URL of the site you would like to allow pop-ups from and click Allow. WebCampus is used in the example below because it is a site at UNR that requires pop-ups to function properly.
Other things to check:
Add-ons and Toolbars may also interfere with websites working properly. You can bypass these potential problems by starting Firefox in Safe Mode. Firefox Safe Mode is a Windows only option. To access it, click the Start button, then ‘All Programs’. Find and click on the ‘Mozilla Firefox’ folder and there should be an option called ‘Mozilla Firefox (Safe Mode)’. Click that icon to start Firefox in safe mode.
The website you are trying to use may not display or operate properly if your anti-virus software is integrated into your web browser. Check your anti-virus documentation and temporarily disable it to see if that resolves the issue.