From MozillaZine Knowledge Base
Adobe Reader or "Adobe Acrobat Reader" is an application that allows you to view and print PDF files. It includes a browser plugin for viewing PDF files directly in a web browser such as Firefox or Mozilla Suite.
Important: Outdated versions of Adobe Reader contain security vulnerabilities. See the Adobe Security bulletins and advisories page for links to Adobe Reader security advisories, which include update instructions.
Adobe Reader plugin
If you are having problems with the plugin such as browser hangs or crashes after viewing a PDF file, or if the Adobe Reader plugin loads very slowly, make sure you are using the latest version of Adobe Reader for your operating system and install any available updates.
Speeding up PDF display
Adobe Reader 6 and the browser plugin automatically load a large number of components when they are opened. These are memory hogs and can cause the plugin to load very slowly. Many Adobe Reader 6 issues have been resolved by upgrading to the latest Adobe Reader version, currently 8.0 on Windows and Mac and 7.0.9 on Linux. If upgrading doesn't help or if you don't meet the system requirements for the latest version, try one of these workarounds:
Adobe Reader Speedup: The Adobe Reader Speedup program disables many of the unnecessary components. If Adobe Reader is not installed in the default location, you will have to change the setting in Adobe Reader Speedup's settings. This is easily done by using the Browse button in the program to point it to the correct location.
Manual method: As an alternative, you can use the following manual procedure: :
Disabling the browser plugin
You can disable the Adobe Reader browser plugin and force .PDF links to open the associated program as an external helper application by using one of the methods below:
After closing Adobe Reader, open your Mozilla application’s installation directory, open the Plugins folder and ensure that the file "nppdf32.dll" is not present. If it is, remove it (or rename "nppdf32.dll" to "Xnppdf32.dll"). Failing to remove or rename this file may cause the browser to hang when attempting to open a PDF file.
Note that Mozilla applications may use plugin scanning to locate the Acrobat Reader plugin. You can prevent this by finding and renaming all instances of "nppdf32.dll" on your computer. Alternately, you can disable the plugin scan via about:config or via the user.js file by modifying the value of the preference plugin.scan.Acrobat from the default 5.0 to a value greater than the version installed, e.g., to 8.0. Advanced users may prefer to open the relevant configuration file and change the preference line
Method 2 (Firefox only)
Open the Tools -> Options menu and select the appropriate option for your Firefox version:
Saving PDF files to disk
You can save PDF files to disk and then open them without using a PDF viewer plugin by right-clicking links to PDF files and choosing "Save Link As".
To make your browser automatically save all PDF files on which you left-click, go to "Tools -> Options -> Downloads -> File Types". Scroll to PDF, press "Change Action" and then select "Save to disk". PDFs will now be downloaded to a folder for opening in Reader separately. Note that this procedure will not work if PDF is not currently listed as a recognized file type. Instead, you should disable the plugin as described above.
Using an alternative PDF viewer
Alternative PDF viewers are available, such as the Foxit Reader (freeware, for Windows, Linux, U3). Other PDF viewers are listed here. It's possible that some PDF files may not work and some functionality may be missing in viewers not made or supported by Adobe. You may wish to keep your Adobe Reader program installed and just disable the Adobe Reader browser plugin (see above) when adding an alternative PDF viewer . That way, if problems arise, you can save the PDF file and open it by right-clicking, selecting "Open with" and choosing your Adobe Reader program.
PDF download (Firefox extension)
The PDF Download extension gives Firefox users multiple options for handling PDF files such as viewing as HTML, opening within the browser or opening within the default or preferred PDF viewer.