This turned out to have been partly-caused by the patch that landed in bug 1923251. Masayuki and I backed that out earlier today, which will probably make this no-longer-reproducible in tomorrow's nightly, hopefully. (bug 1923251 is what turned out to be responsible for deleting the all-important `<br>` element that I referenced in comment 5. At the time I wrote comment 5, I thought my "good" sessions (where the `<br>` persisted and propped up its neighboring space character) were a result of some Gmail A/B testing, but in fact I'm pretty sure those "good" sessions were just environments where I was running a slightly-out-of-date nightly.)
Bug 1925606 Comment 10 Edit History
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This turned out to have been partly-caused by the patches that landed in bug 1923251. Masayuki and I backed that out earlier today, which will probably make this no-longer-reproducible in tomorrow's nightly, hopefully. (bug 1923251 is what turned out to be responsible for deleting the all-important `<br>` element that I referenced in comment 5. At the time I wrote comment 5, I thought my "good" sessions (where the `<br>` persisted and propped up its neighboring space character) were a result of some Gmail A/B testing, but in fact I'm pretty sure those "good" sessions were just environments where I was running a slightly-out-of-date nightly.)