1. Why doesn’t my page look right in Mozilla?

Mozilla is designed to support Internet standards as thoroughly as possible. Some sites have pages coded around standard quirks of older browsers (rather than standards-compliant code that all current browsers, e.g. Mozilla, Netscape 7, and Microsoft Internet Explorer 5.5 or later, can read), and some sites even use erroneous browser sniffing to block Mozilla. If this is the case, you should contact the site webmaster about updating their server configuration and page code.
2. I’m trying to view a file on a website, and the address looks correct, but all I see is a bunch of garbled garbage on my screen.

You can usually work around this by right-clicking the link, going to ‘Save Link Target As’, saving the file to disk and then viewing the saved file locally.

The typical cause is that the web server is serving the file as a plain-text file. Contact the site administrator about the misconfiguration.
3. My bank site blocks Mozilla!

Some financial-institute sites block access from Mozilla because the site administrators do not understand the security features in Mozilla. Mozilla is secure and does not save sensitive information such as password if the site choose to prevent it. Talk to your bank about removing the block on Mozilla.
4. I cannot open Mozilla / my profile. Mozilla says the profile is in use.

Look in your profile directory for file called parent.lock, lock, or .parentlock. Delete the file. (The file is created on start-up to prevent multiple instances of Mozilla or Mozilla-based browser from accessing the same profile simultaneously. The file is destroyed on exit.)
5. Why can’t I access secure (https://) websites? (Linux)

The most likely cause is that you did not install the Personal Security Manager when you installed Mozilla. Uninstall Mozilla and reinstall with it included. You can also install it directly.
6. I’m using a transparent proxy (such as Junkbuster) and I’m having weird browsing problems. What’s happening?

Some transparent proxies (including some versions of Junkbuster) do not handle HTTP/1.1 properly. The first thing to try is to go to Edit | Preferences | Advanced | HTTP Networking and select ‘Use HTTP 1.0’.
7. Middle click (or Ctrl+click) on a link does not open a new tab.

The option for opening links in new tabs with middle-click (or Ctrl+click) is off by default. To turn it on, open the Edit menu and choose Preferences. Navigate to Navigator | Tabbed Browsing catagory in the left pane. Then check Middle-click, Control+click or Control+Enter on links in a Web page.
8. I love a theme I’m using, but weird things are happening with it. Is there a way to fix it?

Some third-party themes lack a file called fakeAccount.css. The absence of this file can cause buggy behavior, such as windows failing to minimize properly. Check if a more recent version of the theme is available.

If you feel comfortable with experimenting with theme files, create an empty file called fakeAccount.css and put it into the JAR of the affected theme. JARs are standard zip files, so you can open and rewrite them using the zip utility of your choice. Be sure to keep a copy of the original JAR file on hand in case of problems.

If this does not fix the problem, and the problem does not occur after uninstalling the theme and using Classic or Modern, you may wish to report the problem to the theme’s author.
9. I tried to install a Mozilla add-on XPI directly from a web page, but clicking the ‘Install’ link didn’t work.

You need to switch on both JavaScript (in Edit | Preferences | Advanced | Scripts & Windows) and Software Installation (in Edit | Preferences | Advanced | Software Installation) for this to work.

If it still doesn’t work, try downloading the XPI and installing it directly.
10. I have downloaded a Mozilla add-on (.xpi) file, but can’t figure out how to install it.

Check that Software Installation is enabled, then open the file in Mozilla by dragging it to the browser window; by opening it using File | Open File; by typing the location into the location bar; or (in Windows) by double-clicking on the XPI file and telling Windows to open .xpi files using Mozilla.
11. How do I uninstall something installed from an XPI?

There is not yet a method of automatically uninstalling XPIs other than themes. However, when you have uninstalled Mozilla prior to installing a new build, you can manually remove the unwanted XPI.
12. The sidebar comes up empty.

Try closing and opening the sidebar again, with the F9 key. If this fails, it may be a corrupt profile – create a fresh profile and see if the sidebar works with that.
13. Help! I can’t access my e-mail any more!

The two common causes of e-mail problems in Mozilla Mail are:

1.

The mail summary files (files with the .msf extension) have become corrupted.
2.

Some test builds of Mozilla have been known to improperly compact mail folders, rendering the mail within unreadable by Mozilla Mail/News.

In the first case: exit Mozilla (including Quick Launch), find the folders in your user profile that contain your e-mail (the Mail and, if you use IMAP, ImapMail folders). Back up your mail folders, and delete the .msf files. Do not delete files that appear without any extension – these are the files that contain your actual e-mail. Restarting Mozilla Mail should automatically generate new summary files.

In the second case: the mail files are stored as plain text, so you can try opening the mail files with a text editor (or word processor) to recover the text of your e-mail by hand.
14. I use GNOME. I installed Mozilla from a mozilla.org binary, and now Nautilus isn’t working properly.

If Nautilus has been configured to use the Mozilla Gecko rendering engine, installing a mozilla.org binary on top of that may cause odd problems and conflicts. You should use the package of Mozilla supplied by your Unix or GNU/Linux distribution, as their version should work properly with their package of GNOME.

If you want to install a testing build of Mozilla, install it to a non-default location (e.g., in your home directory), and leave the system defaults to use the older distribution version.