Here's a guess: Firefox can be rather particular about height rules that use a percentage. A lot of sites will set an embedded object to a height of 100% but when Firefox tries to compute 100% by checking the height of each containing element all the way up to the body, if it encounters an element that has an indeterminate height, the computation may stop leaving the embedded object with the default height of 300 pixels.

Now... if this problem affects one copy of Firefox much more than another one, I would suspect that the page is not loading completely, or is being modified, perhaps by an add-on or custom style rule.

Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Thank you for the suggestion. I tried safe mode, it didn't help. It is strange that I only have the problem on some computers and not others, although safe mode doesn't help. Maybe there is a setting that was changed on the computer that does work, but I don't know what it would be. Is there a way to change the default height of embedded objects?

bazza36 said

Is there a way to change the default height of embedded objects?

Maybe. It's easy to declare custom style rules, but that may break sites that are working correctly. I can't think of an automatic approach that is safe, meaning, not creating more problems than it solves.

Could you give a couple links to pages that have this problem, assuming they don't require a login (and are family friendly)?

A lot of the problem was with pdf's, that didnt help when addons were disabled. I am using a different pdf reader, and changed one of the settings in Firefox, but I don't remember exactly what it was. Something with page setting, and it works better. I assumed it wasn't just pdf's, because I have the problem with a work site, but that requires a login. Solving the pdf's is a lot of the problem, and the other website Ill just live with. Thanks for your help.

Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

• Use a compressed image type like PNG or JPG to save the screenshot
• Make sure that you do not exceed the maximum size of 1 MB

Start Firefox in Safe Mode to check if one of the extensions (Firefox menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox menu button/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes