The release of Firefox 104 in August gave users the ability to annotate PDFs, e.g. sign PDFs directly in the browser, and save them. Here’s how:

- Open a PDF in Firefox, i.e. drag it into the Firefox Window, or right click on the file and select ‘Open with’ and choose Firefox.

- In the top right corner of the PDF window click on the ‘Add Free Text Annotation’ icon (a ‘T’ symbol). 

- Click on the page and start writing. You can change the text colour and size.

- Also top right (a pen symbol), click on the ‘Add Link Annotation’ icon to use a virtual pen to annotate or sign a document freehand. The colour and line thickness can be adjusted.

- To save an annotated PDF, click on the ‘Download’ button in the toolbar.

- To disable annotation editing, click on the arrow symbol (top right).

If Firefox browser doesn’t yet have the annotation options:

- Type about:config in the address bar, press Enter, click on ‘Accept the risk’ and ‘Continue.’

- Look for the preference pdfjs.annotationEditorMode, click the button next to it, and change the value to 0 (zero).

- Click the tick box to confirm and restart Firefox.