vaidikkp/zamboni — comment on commit 56b9141f9e7455e317c50869dbf8ce57df0a682c
File: media/css/legacy/main-mozilla.css line 1346
By vaidikkp:

In LTR, the "Add to Collection" text comes in two lines with the icon on the left to "Add" in the first line. Now in RTL, this icon should come on the right of "Collection". When locale is an RTL language and with "Add to Collection" in two lines, it is not possible to place the icon on the left of "Collection".

`inline-block` ensures that the text comes in one line and then correct positioning of icon is possible.