Update broke SeaMonkey compatibility

After an update today (from 93dfdb2fc to 54aeb6f59) Tiny Tiny RSS no longer works with SeaMonkey 2.49.4. When I log in, I get the following “Fatal Error” dialog:

Fatal Error

Browser feature check failed: window.requestIdleCallback not found.

Additional information:
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.4

Tiny Tiny RSS still seems to work with other browsers.

tt-rss version (including git commit id):
v18.12
54aeb6f5928a03e5a44da48629ebd8dea6fde941

Platform (i.e. Linux distro, PHP, PostgreSQL, etc) versions:
Raspbian 9.6
PHP 5.6.33
PostgreSQL 9.6+181+deb9u2

A post was merged into an existing topic: TypeError: window.requestIdleCallback is not a function