Hi Jeffrey!

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Thanks!

Thanks for your prompt reply. Followed your directions but problem persists even in safe mode. I thought that solution would work also.

You may have accidentally zoomed web page(s). Reset the page zoom on pages that cause problems.

• View -> Zoom -> Reset (Ctrl+0/Command+0 (zero))

• https://support.mozilla.org/en-US/kb/how-do-i-use-zoom

If you have made changes to Advanced font size settings like increasing the minimum/default font size then try the Default font size setting "16" and the Minimum font size setting "none" in case the current setting is causing the problem.

• Options/Preferences -> General: Fonts & Colors -> Advanced -> Minimum Font Size (none)

Make sure you allow pages to choose their own fonts.

• Options/Preferences -> General: Fonts & Colors -> Advanced
  [X] "Allow pages to choose their own fonts, instead of my selections above"

It is better not to increase the minimum font size, but to use an extension to set the default page zoom to prevent issues with text not getting displayed properly.

Hi Jeffrey, that particular one is a video (attached screenshot).

Firefox's Content Blocking feature might block some videos that are access through tracking sites.

Do you see a shield icon toward the left end of the address bar, near the lock icon? More info on managing the Tracking Protection feature in this article: Content Blocking.

Otherwise, hmm, do you use any external filtering web software (security, parental controls) that might be blocking some videos?

The screen shot, to my knowledge and compared to IE of same page, is not a video. There are some video links on various pages that do indeed show up as such-same w/ images. These blank sections correspond to nothing I can see on IE when comparing the same article.

Can you post a link to a publicly accessible page (i.e. no authentication or signing on required)?

My apologies! When I turned off my ad blocker, lo and behold, video ads appeared. Previously, I had started in SAFE mode and gaps still appeared. Presumed Ad Blocker Plus was disabled. Odd fact though, on IE w/ same ad blocker there are no gaps on same page and no indications that an add was even there. Thanks for your help.