Mozilla is currently working to improve the PDF viewer within Firefox. According to the latest leaks, it will soon include new features. This feature is currently only available in the nightly builds, but you can add notes to documents.
Noting that notes can be handwritten or text, You can alter the font and color of your text as well as the lines before and after creating them. These features are not yet available in the final release.
Similar features are already available in Microsoft Edge. There are also PDF editing tools. Mozilla seems to be on a similar track.
The company had earlier commemorated the end of support and “death” of Internet Explorer 11 in a unique way. Mozilla sent a cake containing the browser logo and the phrase “You’re the IE6ing on it” (“You were like the icing on top of the cake”)
Browser support was discontinued on June 15th.