hello Lillow, the pdf viewer is still somewhat experimental and under very active development - you could try if the same error is occurring in the current development version, which you can download as an addon from http://mozilla.github.io/pdf.js/extensions/firefox/pdf.js.xpi

in case it has the the same rendering problems, you could then file a bug report at https://github.com/mozilla/pdf.js/issues (a github account is necessary for it though) - please also provide a sample document where the error is apparent!

It could be that the text the reader is displaying has characters from another language. You will have to look at the document origin.

This problem is in our corp. We couldn't install any addons, it's out of policy. On three comps all ok. On this comp, if I start browser in safe mode - all ok. I tried to get off all addons and plugins, one at a time and so on, but it isnt works. I deleted his profile - none. I reinstall FF - none. I don't thik the problem is in comp, cause in safe mode - all ok. And Fillipp - unfortunally I can't send the document - it's privacy =(

if it works in safemode maybe it's an issue with hardware acceleration - you could disable it under firefox > options > advanced > general.

Are there embedded font used in the PDF file?

This can also be a problem with the font that is used to display the text.
You can check the font used for text and select "Inspect Element" in the right-click context menu to open the Inspector and go in the right pane to the Font tab.

You can try different default fonts and temporarily disable website fonts to test the selected default font.

• Tools > Options > Content : Fonts & Colors > Advanced
• [ ] "Allow pages to choose their own fonts, instead of my selections above"