Cristian Comorasu, QA [:ccomorasu], Releae Desktop QA - Please contact mboldan@mozilla.com Reporter
	Description • 6 years ago

[Affected versions]:
 Fx 52.7.3
 Fx 60.0b8
 Fx 61.0a1

[Affected platforms]:
 Ubuntu 14.04 LTS
 Windows 10 x64
 mac OS X 10.13.2

[Steps to reproduce]:
 1. Launch Firefox.
 2. Go to http://ilab.engr.utk.edu/iLabDocs/Epilog/BMP%20sample%20files/lady3.bmp .
 3. Zoom out to 30%(maximum).

[Expected result]:
 The zoom goes smoothly.

[Actual result]:
 Between 50% and 30% the image glitches.

[Regression range]:
 This is not a recent regression as I could reproduce it using Fx 31.0a1.

[Additional notes]:
 a. This issue occurs only with .bmp photo format.
 b. Gif with the issue: https://imgur.com/a/p1y1H

	Cristian Comorasu, QA [:ccomorasu], Releae Desktop QA - Please contact mboldan@mozilla.com Reporter
	Comment 1 • 6 years ago

I manually searched for the regression range as was unable to find the older builds. Here are the results:

Last good: 2009-10-14 - 3.7a1pre
First bad: 2009-10-15 - 3.7a1pre

	Daniel Holbert [:dholbert]
	Comment 2 • 6 years ago

I think what's really happening here is:
 - The image is too big to fit on your monitor (at 100% zoom level), so we apply a scale to it (in my titlebar, this shows up as "Scaled  (46%)" on the initial rendering).
 - When you're manually zooming out, we're applying a zoom factor at a separate level (effectively zooming the whole page, i.e. increasing the size of the viewport).
 - When you cross the threshold where the image would fit in the (zoomed) viewport without any scaling needed, we apparently remove the scaling.  (You can see that this happened because "Scaled" gets removed from the title bar.) Visually, this ends up looking like the image gets zoomed in again.

I don't think this has anything to do with BMP in particular -- it's probably just extremely large images in general.