If you're using foxit reader - upgrade to the latest version (4.3?). After restarting FF, PDF files display perfectly/quickly.

Foxit reader is Windows only

This happens to me as well, but only if FireFox 4 is already open. If Firefox is not running it will load the PDF file properly. I have had the issue with Adobe Reader 9 & X (10) and the issue continues whether or not PDF files are configured to open within the browser.

the thing is: 1.load adobe acrobat reader or adobe reader(i think u already installed it); 2.goto tools->options->applications and chose like the image below.

I don't know about foxit reader, anyhow it turned out that you can resolve the problem either installing the new version of acrobat reader (10.**) or just replacing the acrobat browser plugin (nppdf32.dll) of acrobar reader 9.* with the one from version 10.* This plugin usually is under the mozilla folder in C:\ programs\....\Mozilla Firefox\plugins. After doing that pdf worked smoothly.

The problem was that being in a work environment I couldn't isntall acrobat reader 10, so I had to install it at home then copy the plugin file from home pc to the one in my office..

Reinstalling Reader 10.* does not fix the problem with Mac OSX 10.6 and Firefox 4. I have tried numerous option and nothing works.

I am going to move to Safari as my prime browser since I open PDF files on a regular part of my work.