Affected versions

• Firefox 89.0a1 (BuildId:20210408215439)
  Firefox 88.0b8

Affected platforms

• macOS 11.2
  macOS 10.13

Unaffected platforms

• Windows 10 64 bit
  Ubuntu 18.04

Steps to reproduce

1. Reach this reddit link
2. Double tap on anything inside the post.

Expected result

• Double tapping should zoom in to the area.

Actual result

• Double tapping does not zoom in on anything inside a post on reddit

Suggested Severity

• I suggest an S2 severity because inside a high traffic top site the feature is not working.

Additional notes

• On the main page of reddit the feature works as intended only inside posts does it stop working.
  Pinch to zoom works as intended inside posts.

It works for me. Maybe you have the old or new version of reddit?

Hmm, that's can't be it, I tried the old version of reddit and double tap works for me there too.

Hello,

Unfortunately the screen capture is to big for bugzilla, I added a screencapture that can be viewed here

I tried to follow the video as closely as possible and used a fresh profile, double tapping always worked for me.

That's weird because a colleague could reproduce on the macOS 10.13 so it's not specific to my laptop.
I just tried again with a clean profile and I can still reproduce this issue.

Maybe you are getting different ads then me and the ads are causing the problem. What if you install an ad blocker?

I've tried on 3 different macbook pro's now, all on 10.15 (I don't have anything else) and I can not reproduce on any of them.

Ok interesting thing just happened.
I installed Ublock Origin, blocked adds on a post double tapped several times in different areas and nothing happened. Restarted browser with (CMD+Shit+J)+(CMD+option+R) the browser opened on the same post and I was able to double tap to zoom. Then I returned to the main page and clicked the post again, and now I cant double-tap to zoom.

Okay, seems like I can reproduce if I load the original page, goto the main subreddit page and click on the post again.

For some reason the page is inside position fixed, similar to bug 1703804, so very likely they have the same root cause.

Simple testcase, just need a scrollable element (that has a displayport, ie it has been recently scrolled) to reproduce this.

Should be fixed now.

Hello

I can confirm that this issue is fixed in 90.0a1 (Build ID:20210421212740)

Hello,

While confirming that this issue is indeed fixed on 89.0b3 it seems that the fixed caused a new issue bug 1707235. I made filled a separate bug for the issue.