Adjust min-width for compatibility select (bug 1093936, bug 1102929)

https://bugzilla.mozilla.org/show_bug.cgi?id=1093936
https://bugzilla.mozilla.org/show_bug.cgi?id=1102929

Screenshots (note that it was already too small and cutting the text on prod):

**Prod**
![screen shot 2014-12-04 at 15 11 19](https://cloud.githubusercontent.com/assets/187006/5281647/fdff763a-7aff-11e4-983a-7e03c5d47fa1.png)
![screen shot 2014-12-04 at 15 11 31](https://cloud.githubusercontent.com/assets/187006/5281649/fe00aa3c-7aff-11e4-9757-93a66468d2f1.png)

**This PR** (In french, but the lengths of the texts are similar in english)
![screen shot 2014-12-04 at 15 16 53](https://cloud.githubusercontent.com/assets/187006/5281646/fdfbddc2-7aff-11e4-908b-0cf57f814a81.png)
![screen shot 2014-12-04 at 15 16 57](https://cloud.githubusercontent.com/assets/187006/5281648/fdffbb0e-7aff-11e4-8169-1dfc4d0cb271.png)
whitespace