Affected versions

• 84.0a1(2020-11-11), 83.0

Affected platforms

• macOS 10.15;

Steps to reproduce

1. Launch Firefox, access about:telemetry
2. Click on the [Raw Json] button(bottom-left in page);
3. In the newly open tab, copy the link from address bar;
4. Open another tab, paste the link in the address bar;

• in looking for the regression range, some builds were also affected by this on opening and pasting the string in yet another tab(text being pasted then vanishing from the address bar) after half a second;

Expected result

• string is displayed;

Actual result

• string is not displayed in the address bar, browser/tab appears to start lagging as well
• (lagging part might be expected tho due to the size/length of the string);

Regression range

• First bad: 2019-05-28;
• Last good: 2019-05-29;
• Pushlog: URL;

Additional notes

• S4 as suggested severity, as it might be an edge case scenario; however consider increasing it if it applies on other scenarios as well;
• swapping between another tab then to the affected one appears to fix the issue;
• attached recording to illustrate the issue.

Attaching is a document with the used long string.

The "Raw JSON" page isn't part of about:telemetry. Instead it's just a (very) long data URI. Pretty sure this doesn't have much to do with Telemetry... ah, here we go. I can reproduce this issue on my Linux Mint machine running Nightly 20201108 by pasting a text over one million characters in length (the contents of Albert Einstein's wikipedia page pasted over and over) into the address bar.

Oddly, Windows (Nightly 20201112) doesn't have the same issue.