User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170604030205 Steps to reproduce: Nightly 55.0a1 (2017-06-04) (64-Bit) MacOS 10.12.5 STR: 1) Open new window 2) Open some more tabs 3) Shrink the window to very small, so that the arrows appear left/right on the Tabstrip 4) Close all tabs except one tab Actual results: The arrows should disappear. Expected results: The arrows are still there. This is a regression since using a larger drag space on the left side of the tabs. A screencast is attached.

I think the issue is here even with only one tab open. STR: 1) open one tab 2) shrink the window to the minimum size Result: double arrows are visible and it's impossible to close the tab (clicking on the X icon).

I tested with FF29 and the issue is already present, so I don't think it's a regression. When the width is reduced to the minimum, keeping one tab open makes visible the arrows </>. If you increase the width then reduce it again to the minimum, they disappear.

Sorry, but this is definitely a regression. Enclosed a screencast from FF53 showing, that the arrows disappear, when you close the second tab.

And enclosed a further screencast from Nightly 55 showing, that the arrows NOT disappear, when you close the second tab.

Dão, is it possible given the contrast between 53 and 55 as noted in comment #3 / comment #4 this is actually a latent regression from the perf improvements for lazier bounds/size-checking in the tabstrip that you worked on? Maybe we need to rerun something after removeTab() completes, or something?

(In reply to :Gijs from comment #5) > Dão, is it possible given the contrast between 53 and 55 as noted in comment > #3 / comment #4 this is actually a latent regression from the perf > improvements for lazier bounds/size-checking in the tabstrip that you worked > on? Maybe we need to rerun something after removeTab() completes, or > something? No, this is a consequence of bug 1355764, i.e. there's less horizontal space and thus the tab strip doesn't underflow with a single tab in a narrow window. Bug 1349555 might fix this.

Just an idea: A larger min width could may be also fix this. Firefox has the smallest min width compared to Chrome or Safari. Attached a screenshot. Thanks.

(In reply to Mehmet from comment #4) > Created attachment 8874886 [details] > Nightly55_one_tab.mov > > And enclosed a further screencast from Nightly 55 showing, that the arrows > NOT disappear, when you close the second tab. Not on Windows. If you open a 2nd tab then close it, the arrows don't disappear for the only tab open. It's like that for many older versions.