User Agent: Mozilla/5.0 (Windows NT 6.1; rv:90.0) Gecko/20100101 Firefox/90.0

Steps to reproduce:

When a pop-up or second window opens, sometimes everything appears gibberish. No text is readable. I have noticed it after last automatic Firefox update.

The Bugbug bot thinks this bug should belong to the 'Toolkit::Application Update' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Right-click some of the unreadable text and choose Inspect. In the pane that opens, click the Fonts tab on the right. What does it say next to Fonts Used?

It is not a repeatable issue. It happens sometime. I do not know how to repeat this. I will check this "Fonts" detail when this issue happens next time.

I remember similar issues on Android+WR, but maybe I'm misremembering? Maybe Jamie has some ideas of what could be worth trying?

Saurabh, could you please attach your about:support information?

(In reply to Emilio Cobos Álvarez (:emilio) from comment #4)

I remember similar issues on Android+WR, but maybe I'm misremembering? Maybe Jamie has some ideas of what could be worth trying?

We've seen similar in the past when texture uploads have been failing, for various reasons. It's hard to tell if that's what is going on here, though. Lee, why do you think this is SWWR related? Because it occurs in popups?

This issue has not appeared after a few of those incidents. It is possible it is either solved or the root cause that causes it has not been repeated since then.

I keep the pop-ups blocked but my bank (UCO bank) website requires pop-up permission, without which it will not show the login page, so I allow pop-ups for it only. That is where I had first noticed this problem. Then it happened a few more times in its pop-ups and when opening another window of Firefox. This bank's those pop-ups are now rendering well and there is no problem now. Second windows are also opening well.

(Another issue that may have some relevance to this issue:
Crashing had stopped some months back but it has been happening occasionally now. I see it generally when I have more than 20 tabs open. I have Dual Core, 4 GB RAM and Windows 7. More than half of this RAM seems to be used up by Dragon Naturally Speaking and MS Word which are continuously open. The new updated Firefox versions may be requiring a computer with higher configuration.)

P.S. - "Copy raw data to clipboard" and "Copy text to clipboard" buttons on the about:support page are not working (they do not copy any text to the clipboard) so I have copied that page in text form and posting it with "Attach new file".