I've noticed that Nvidia have released a new Win 10 driver set this morning for my GPU but that's not resolved the problem. The Mobo chip set drivers and everything else are all up-to-date with the latest Win 10 build. I'm wondering if one of the fonts didn't install correctly on upgrading to Win 10.
Here's a picture of the issue I'm experiencing, it's most noticeable when using gmail, again this happens using any browser, Edge, Chrome, Firefox and IE.
finally found the issue, Windows 10 doesn't seem to like some of the Helvetica fonts. The one in particular was the Neue set, so if you have these you might want to delete them if they're affecting your browser. Re-installing them doesn't fix the issue.