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We're following the Firefox standard here which is that the sidebar width is controllable by the user. It would be too complicated to control this on a per-sidebar basis

I think it's fine to make it controllable by the user, but can we specify a default?

To clarify (I think perhaps default was the wrong word), I'd like to be able to set an initial width for the sidebar. I think that's a pretty straight forward change. If the user wants to change it from there then that's fine.

It isn't that simple because that default then suddenly overrides the width of all sidebars until the user changes them back again.

Oh, wow, I didn't realize there was one global width. It would be really nice to change this. It doesn't have to be a blocker for a release or anything since it does sound much trickier than I thought, but I do think it's a good goal to eventually do and leaving this bug open would track how many people want such a functionality. If the user has never adjusted the width of the sidebar, is there some default width that is used? Is that a set number of pixels or a percentage of screen size?

The default looks to be 18em, that's for the first time a user ever opens any sidebar. After that it just persists the last width

(In reply to Dave Townsend (:Mossop) from comment #6) > The default looks to be 18em, that's for the first time a user ever opens > any sidebar. After that it just persists the last width And, to be honest, I don't see why some side-bars should be made special, to set their own initial width. Ben - do you have a specific, compelling use case?

I worry very much that the users of our extension are not very sophisticated and will not realize they can adjust the width of the sidebar. If their sidebar is narrow because they were previously looking at other content which needed little width then our larger amount of content might be quite squished when our sidebar is opened. My experience tells me that at this point the users would just abandon the extension as being broken or ugly not realizing they can choose a more appropriate width. We can use responsive design, but even then the user experience could be much worse as important content can only be made so small or is pushed below the fold. I've attached a mock of a Zillow extension that could appear on any other site with housing data. It's showing here on Craigslist. This is a genuinely useful and interesting extension that adds a lot to the page being viewed. There's much more content in the sidebar than in the webpage itself in this case and so it makes sense for the sidebar to be quite large here. And yet, no user will have their sidebar this large by default, which would severely restrict your ability to create this extension. Also, I'd like to be able to put a button in the sidebar which will expand it for showing additional content or collapse it to show a smaller amount of overview content. That is impossible to do without being able to programmatically set the width.

For now we've decided that we're not going to plan on doing this, the UI features in Firefox don't support sidebars as large as you're looking for and managing even an initial size on a per-add-on basis would be difficult. If we hear more call for this once sidebars are in use more then we can revisit this decision.

We started using the SDK for prototypes, but probably couldn't use it for production because of this limitation. The narrow width definitely limits the use cases. Setting an initial size per add-on would make the SDK much more useful for a range of solutions. > And, to be honest, I don't see why some side-bars should be made special Form should follow function. Here are two examples that need a more reasonable width: A Pinterest-like sidebar for collecting images and snippets of text; A split-screen for hunting down accessibility issues for vision-impaired users. > I worry very much that the users of our extension ... will not realize they can adjust the width of the sidebar There is no UI indication that the sidebar is resizable. A user would need to guess this is possible and have the dexterity to grab the hairline divider. This rules out a huge percentage of users.