Open Bug 1037792 Opened 6 years ago Updated 5 months ago

Cannot scroll by dragging the scrollbar thumb after doing Ctrl+A (Select All)


(Firefox :: PDF Viewer, defect, P3)

Windows 7



Tracking Status
firefox68 --- affected
firefox71 --- affected


(Reporter: kenkon, Unassigned)


(Whiteboard: [pdfjs-c-ux])

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0 (Beta/Release)
Build ID: 20140605174243

Steps to reproduce:

1. Open any PDF (e.g.
2. Right-click and choose "Select All" or do Ctrl+A
3. Try dragging the vertical (or horizontal) scroll bar's thumb.

Actual results:

1. The document is opened.
2. Everything is selected including text that is not part of the PDF document but is part of the viewer.
3. The thumb does not move. The page does not scroll. The mouse pointer icon changes to an interdiction sign (black circle with diagonal line). An image preview of the page follows the mouse pointer until the left mouse button is released.

Expected results:

The page should scroll by dragging the thumb. All other scrolling methods work.
QA Whiteboard: [bugday-20140714]
Component: Untriaged → PDF Viewer
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:34.0) Gecko/20100101 Firefox/34.0

Reproduced using latest Nightly 20140727030204.
Ever confirmed: true
Also reported at and, and blocked by bug 734180 and bug 739396
Priority: -- → P3
Whiteboard: [pdfjs-c-ux]

I can reproduce the bug in Firefox 68 on Windows and Linux, but it is also possible to get the same behaviour of the scrollbar by being a bit imprecise with the mouse click at the start of an attempt to click-and-drag of the scrollbar. Click on the grey background of pdf.js, and drag from there onto the scrollbar. It seems this causes something in the pdf.js UI to become invisibly selected, putting the software into the state where the bug occurs. I find that selecting some text in the PDF or clicking anywhere on the page to clear the problematic invisible selection restores normal scrolling behaviour.

In the buggy state, the scrollbar scrolls a small distance before abruptly halting the scroll, at which point the mouse cursor changes. On Windows, the cursor changes to a "not-allowed" cursor, as described in the original bug report. On Linux, the behaviour is identical except it changes to a "grabbing" mouse cursor. This matches the cursors used by Firefox on these platforms when dragging selected text over an item that the selected text cannot be dropped onto.

Reproduced on latest Nightly build 71.0a1 (2019-09-12) on Windows 7 x64.

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