Text Fragments: Make test for opening a link in a new tab more robust.
There were intermittent failures caused by the scroll position being unexpected. However, this test should only ensure that scrolling happens, therefore the assert condition can be changed.
Differential Revision: https://phabricator.services.mozilla.com/D219760
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1914161
gecko-commit: 920049a49f2c13ab6818212bf3d48b2f5ac5ca68
gecko-reviewers: dom-core, farre