HI Jigg, In the past this may have been caused by Adobe Flash, can you disable this plugin and see if it makes a difference?

Then I would suggest you try Firefox in Safe Mode -

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.

same results with flash disabled and safe mode, fonts appear lighter, anti-aliased, smeary, choppy and discolored, just very strange

jlgg said

same results with flash disabled and safe mode, fonts appear lighter, anti-aliased, smeary, choppy and discolored, just very strange

Did you also try the last part of guigs' suggestion :

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  :

https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

In case the above doesn't do the trick, would you give this a try please :

Type in the address bar   about:config   (press Enter) (promise to be careful, if aksed) Type in the search bar :   gfx.font_rendering. then look for the preference :

gfx.fonts_rendering.cleartype_params.rendering_mode

Right-click and choose   'Reset'

thanks, I can't reset it as it is at the apparent default of -1, is there a different value I can set?

ok, a bit better but not perfect, I changed gfx.font_rendering.fallback.always_use_cmaps to true, fonts still lighter than before but not as choppy now

A complete stab in the dark, but worked for others :

In   about:config   look for the preference : gfx.direct2d.disabled   and change it's value to   true

(and leave hardware acceleration enabled)

If that doesn't work either :   change the value back to   false

This could be related with the recent switch in Firefox 52+ from Cairo to Skia for canvas/content rendering.

Firefox 52+ has changed from Cairo to Skia for canvas/content rendering.

• https://www.mozilla.org/en-US/firefox/52.0/releasenotes/
• When not using Direct2D on Windows, Skia is used for content rendering

You can modify these gfx.*.azure.backends prefs on the about:config page to revert to the old font rendering swap the skia,cairo order to cairo,skia or remove the skia and leave cairo.

• gfx.canvas.azure.backends = direct2d1.1,cairo,skia
• gfx.content.azure.backends = direct2d1.1,cairo,skia

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

thanks, cor-el, I had actually found that solution before posting here and had tried it both ways you suggest, and it did not make a bit of difference, even when you'd think it should have...I changed it back to the default skia,cairo but maybe now that I have changed the other switche will try it again..

Ok, so far, changed gfx.direct2d.disabled to true, enabled hardware acceleration (which I had turned off per other solutions and forgot to turn back on), kept gfx.font_rendering.fallback.always_use_cmaps as true, changed skia,cairo to cairo,skia, then changed it back again since the individual letters looked strange and I am leaving it because I can't deal with it anymore and I thank everyone for all their help and work and suggestions.