Thought so, the image didn't upload. Here it is again

Type about:preferences#content<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own.

You can check for corrupted and duplicate fonts and other font issues: http://www.thexlab.com/faqs/multipleappsquit.html - Font Book 2.0 Help: Checking for damaged fonts http://www.creativetechs.com/iq/garbled_fonts_troubleshooting_guide.html

Could you check whether any font rendering preferences have been modified from their default values:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste font_r and pause while the list is filtered

(3) If any are bolded and "user set" you can right-click > Reset them

You probably need to exit and start Firefox back up again to see any difference.

Blocky character edges can point to a change to the gfx.font_rendering.cleartype_params.rendering_mode preference. Here's my understanding of what the numbers do (as of Firefox 45):

//     -1 or 0 = use default for font & size;
//     4 = Natural;
//     5 = Natural Symmetric

=> Sub-pixel anti-aliasing/positioning

//     1 = aliased;
//     2 = GDI Classic;

=> GDI emulation (whole pixel rendering)

//     3 = GDI Natural Widths;

=> GDI emulation with natural widths (?)

Hi FredMcD

The setting you suggested was already set. I'm not sure about the links, they look like they are for Mac OS?

Hi jscher2000

I've looked at the information on the about:config but everything you have suggested seems to be set.

Thanks Any other suggestions?

Just noticed this problem seems to be reflected in Thunderbird too

I hope that helps narrows it down

The Graphics report under your Question Details > More System Details looks good, so it's hard to understand the source of the problem. Everything seems to be in place for Firefox to apply ClearType to the downloadable web font (Open Sans) used on this site.

Are there problems with other webfonts? For example:

Roboto: https://www.google.com/fonts/specimen/Roboto

Roboto looks a bit choppy too. If I go to https://www.google.com/fonts and look down the list they all look choppy but the "add to collection" button font looks fine.

Looking at the top of firefox it looks like its spread up there too.

Baring in mind that other browsers are fine and windows system fonts all look good this seems to be effecting only firefox in a massive way.

Thanks jscher2000 for getting back to me. At this point I'd probably be looking at reinstall but thunderbird is the same so how can something have an effect globally across mozilla products.

It could be a compatibility glitch with your Nvidia driver software. When accelerated features do not work correctly, but do not cause crashes, it may fail to be noticed during testing.

You may want to check whether graphics card/chipset driver updates are available for your system. This article suggests safe ways to do that: Upgrade your graphics drivers to use hardware acceleration and WebGL.

NVidia driver is on 353.54 with an update to 364.72 available. I'll download and install and report back

NVidia Drivers are now at the latest version 364.72, problem sorted but it doesn't seem to be drivers. I re-applied the clearFont in windows and recalibrated the font output too.

Strange things are happening with Windows 10 for me at the moment as default browser cannot be set. Perhaps there's a gremlin in here running around :/

Thanks very much

https://www.bing.com/search?q=change+default+browser+windows+10&pc=MOZI&form=MOZSBR