Here are a few quick and easy ways to install Firefox add-ons manually. They have all been confirmed on Windows only. Feel free to contact me (Ken) if you can confirm these methods on Mac and/or Linux.
Install a Firefox Extension Manually (Also see Install a Firefox Theme Manually)
Download the extension to your computer. If a download option isn't available, right click on the extension's install link and select "Save Link As..". Be sure not to change the file extension. A Firefox extension will be a .XPI file.
Once you have downloaded the extension, there are several ways that you can install it. Some are quicker than others, you'll just have to pick the one that you like the most.
With Firefox open, hit Ctrl+ O (or Cmd+ O) > browse to the extension > double click the extension (or select Open) > Install Now.
If you have MR Tech Toolkit installed, just hit Alt+ X (or Alt+ M for a theme) > double click the extension(s) (or select Open) > Install Now. You can select and install multiple extensions at once.
Drag the extension to the instance of Firefox on the taskbar > wait for Firefox to appear > drop onto the browser window > Install Now.
Drag the extension to the Firefox desktop (or other) program shortcut. If Firefox is running, you'll see the Software Installation window appear > Install Now. If Firefox is not running, it will start up and the Software Installation window appear > Install Now.
If you have a Firefox desktop shortcut with -no-remote -p appended to it (allows for running multiple instances of Mozilla apps), you can install the extension into whatever profile that you'd like.
There's a hidden Install extension button in Firefox. To reveal it, type about:config into the location bar, hit enter, click on the button that reads "I'll be careful, I promise!", paste extensions.hideInstallButton into the Filter field, right click on the Preference Name (or anywhere else), and select Toggle so that the Value is false.
The Install button will be visible at the bottom of the Add-ons manager (a restart is not necessary). The Install button allows for installing extensions only.
Another quick and easy way to manually install Firefox add-ons (both extensions and themes) is to get the Install Toolbar Button.
Once installed, go to View > Toolbars > Customize (or right click on any toolbar other than the Bookmarks one) and drag the Install toolbar button to the toolbar of your choice.
To use, simply click on the Install button, the install add-on window will open, browse to the extension or theme that you want to install > double click the add-on (or select Open) > Install Now.
After installing the Install button, it will appear as Custom Toolbar Buttons in the Add-ons Manager.
Get the Install Add-ons Toolbar Button (Firefox 3.5 - 3.7a1pre)
Click on the link above.
The software installation permission prompt will appear.
Select Allow
Select Install Now
Restart Firefox
More Toolbar Buttons
Install a Firefox Theme Manually
To manually install a Firefox theme into Firefox, download the theme to your computer. If a download option isn't available, right click on the theme's install link and select "Save Link As..". Be sure not to change the file extension. A Firefox theme will usually be a .JAR file.
Open the Firefox themes manager by going to Tools > Add-ons > Themes.
Drag the theme file from wherever you downloaded it to onto the Themes Manager.
The Software Installation window appear, click on Install Now, then restart Firefox.
Selecting a Theme
Go to the Firefox drop down menus at the top of the browser. Select Tools > Add-ons > Themes > select a theme, click on Use Theme, then restart Firefox. Your selected theme will be visible after Firefox is restarted.
More Toolbar Buttons
The Install Toolbar Button is provided by Michael Buckley the developer of the Toolbar Buttons add-on (and many others) that offers more than 100 toolbar buttons for Firefox (also available for Thunderbird and Sunbird). You can also use the Custom Toolbar Buttons Maker to choose individual toolbar buttons for Firefox, Thunderbird, or Sunbird.
